Fix warnings regarding non-existent package

[jonorossi]

Update minimum Castle Core version to 4.1.0 to fix package restore
warnings that turn into errors (resulting in build failure) because the
version of System.ComponentModel.TypeConverter referenced by Castle
Core does not exist.

Fixes #321

[jonorossi]

This change fixes the failed compilation, however introduces some failing unit tests because the assembly version of the Castle Core assemblies is no longer 4.0.0.0. We need to get castleproject/Core#288 fixed and released, and bump the minimum version again otherwise consumers of Windsor will run into these errors on .NET Framework, we don't want users to have to deal with binding redirects.

Castle.MicroKernel.SubSystems.Conversion.ConverterException : Could not convert string 'Castle.Services.Logging.Log4netIntegration.ExtendedLog4netFactory,Castle.Services.Logging.Log4netIntegration,Version=4.0.0.0, Culture=neutral,PublicKeyToken=407dd0808d44fbdc' to a type.
----> System.IO.FileLoadException : Could not load file or assembly 'Castle.Services.Logging.Log4netIntegration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=407dd0808d44fbdc' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)