Convert solution to the new csproj format

Although the [documentation (Additions to the csproj format for .NET Core)][1] seems to imply that this is a .NET Core feature, it works with .NET Framework too and is much easier to maintain.

With this commit, the OctoPack feature is gone because the new .csproj format is not yet supported by OctoPack. Here is the [suggested workaround][2]:
> We have this support on our radar, but don't have an ETA at this stage.
In the meantime, you could try running `dotnet publish` and then run `octo.exe pack` against the publish output folder.

[1]: https://docs.microsoft.com/en-us/dotnet/core/tools/csproj
[2]: OctopusDeploy/Issues#3822 (comment)

src/SbManager.IntegrationTests/RestTestBase.cs

@@ -1,5 +1,4 @@
-using System.Configuration;
-using System.Net;
+using System.Net;
 using RestSharp;
 using Shouldly;
 
@@ -13,7 +12,7 @@ public abstract class RestTestBase
 
         protected void GivenARestClient()
         {
-            Rest = new RestClient(ConfigurationManager.AppSettings["BaseServiceUrl"]) { FollowRedirects = false };
+            Rest = new RestClient("http://localhost:8062") { FollowRedirects = false };
         }
 
         protected void GivenAGetRequest(string path)

src/SbManager.IntegrationTests/SbManager.IntegrationTests.csproj

@@ -1,102 +1,15 @@
-<?xml version="1.0" encoding="utf-8"?>
-<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
-    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
-    <ProjectGuid>{3EE2A8CD-4EEA-42B1-B1C2-1520D3FAC542}</ProjectGuid>
-    <OutputType>Library</OutputType>
-    <AppDesignerFolder>Properties</AppDesignerFolder>
-    <RootNamespace>SbManager.IntegrationTests</RootNamespace>
-    <AssemblyName>SbManager.IntegrationTests</AssemblyName>
-    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
-    <FileAlignment>512</FileAlignment>
-    <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\</SolutionDir>
-    <RestorePackages>true</RestorePackages>
-    <TargetFrameworkProfile />
+    <TargetFramework>net461</TargetFramework>
+    <Version>1.0.0.0</Version>
+    <Company>GlobalX</Company>
   </PropertyGroup>
-  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
-    <DebugSymbols>true</DebugSymbols>
-    <DebugType>full</DebugType>
-    <Optimize>false</Optimize>
-    <OutputPath>bin\Debug\</OutputPath>
-    <DefineConstants>DEBUG;TRACE</DefineConstants>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-  </PropertyGroup>
-  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
-    <DebugType>pdbonly</DebugType>
-    <Optimize>true</Optimize>
-    <OutputPath>bin\Release\</OutputPath>
-    <DefineConstants>TRACE</DefineConstants>
-    <ErrorReport>prompt</ErrorReport>
-    <WarningLevel>4</WarningLevel>
-  </PropertyGroup>
-  <ItemGroup>
-    <Reference Include="Autofac, Version=3.5.0.0, Culture=neutral, PublicKeyToken=17863af14b0044da, processorArchitecture=MSIL">
-      <SpecificVersion>False</SpecificVersion>
-      <HintPath>..\packages\Autofac.3.5.2\lib\net40\Autofac.dll</HintPath>
-    </Reference>
-    <Reference Include="Newtonsoft.Json, Version=11.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed">
-      <HintPath>..\packages\Newtonsoft.Json.11.0.2\lib\net45\Newtonsoft.Json.dll</HintPath>
-      <Private>True</Private>
-    </Reference>
-    <Reference Include="nunit.framework, Version=2.6.4.14350, Culture=neutral, PublicKeyToken=96d09a1eb7f44a77, processorArchitecture=MSIL">
-      <SpecificVersion>False</SpecificVersion>
-      <HintPath>..\packages\NUnit.2.6.4\lib\nunit.framework.dll</HintPath>
-    </Reference>
-    <Reference Include="RestSharp, Version=105.2.3.0, Culture=neutral, processorArchitecture=MSIL">
-      <HintPath>..\packages\RestSharp.105.2.3\lib\net451\RestSharp.dll</HintPath>
-      <Private>True</Private>
-    </Reference>
-    <Reference Include="Serilog, Version=2.0.0.0, Culture=neutral, PublicKeyToken=24c2f752a8e58a10, processorArchitecture=MSIL">
-      <HintPath>..\packages\Serilog.2.0.0\lib\net45\Serilog.dll</HintPath>
-      <Private>True</Private>
-    </Reference>
-    <Reference Include="Shouldly, Version=2.8.0.0, Culture=neutral, PublicKeyToken=6042cbcb05cbc941, processorArchitecture=MSIL">
-      <HintPath>..\packages\Shouldly.2.8.0\lib\net40\Shouldly.dll</HintPath>
-      <Private>True</Private>
-    </Reference>
-    <Reference Include="System" />
-    <Reference Include="System.Configuration" />
-    <Reference Include="System.Core" />
-    <Reference Include="System.Runtime.Serialization" />
-    <Reference Include="System.ServiceModel" />
-    <Reference Include="System.Xml.Linq" />
-    <Reference Include="System.Data.DataSetExtensions" />
-    <Reference Include="Microsoft.CSharp" />
-    <Reference Include="System.Data" />
-    <Reference Include="System.Xml" />
-    <Reference Include="TestStack.BDDfy, Version=4.1.0.0, Culture=neutral, processorArchitecture=MSIL">
-      <SpecificVersion>False</SpecificVersion>
-      <HintPath>..\packages\TestStack.BDDfy.4.1.2\lib\NET40\TestStack.BDDfy.dll</HintPath>
-    </Reference>
-  </ItemGroup>
-  <ItemGroup>
-    <Compile Include="Constants.cs" />
-    <Compile Include="Properties\AssemblyInfo.cs" />
-    <Compile Include="RestTestBase.cs" />
-    <Compile Include="REST\OverviewTests.cs" />
-  </ItemGroup>
-  <ItemGroup>
-    <None Include="app.config">
-      <SubType>Designer</SubType>
-    </None>
-    <None Include="packages.config" />
-  </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\SbManager\SbManager.csproj">
-      <Project>{c3357d9e-5195-401f-8322-213d3a8cb749}</Project>
-      <Name>SbManager</Name>
-    </ProjectReference>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.7.2" />
+    <PackageReference Include="NUnit" Version="3.10.1" />
+    <PackageReference Include="NUnit3TestAdapter" Version="3.10.0" />
+    <PackageReference Include="RestSharp" Version="106.2.2" />
+    <PackageReference Include="Shouldly" Version="3.0.0" />
+    <PackageReference Include="TestStack.BDDfy" Version="4.3.2" />
   </ItemGroup>
-  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
-  <Import Project="$(SolutionDir)\.nuget\NuGet.targets" Condition="Exists('$(SolutionDir)\.nuget\NuGet.targets')" />
-  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
-       Other similar extension points exist, see Microsoft.Common.targets.
-  <Target Name="BeforeBuild">
-  </Target>
-  <Target Name="AfterBuild">
-  </Target>
-  -->
 </Project>