Update application to run with ASP.Net Core 3.0

[bradleypatton]

Update the .proj file and Startup.cs to compile and run under ASP.Net core 3.0.

Application now runs and opens fine but get the following error when trying to load the Roles grid (similar one for the Users grid)

HomeController line 244:

System.InvalidOperationException: 'The LINQ expression 'OrderBy<ApplicationRole, object>(
source: Where(
source: DbSet,
predicate: (a) => True),
keySelector: (a) => (Unhandled parameter: __propInfo_0).GetValue(a))' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.'

[mguinness]

That could be related to EF Core 3.0 Broke PredicateBuilder which is a regression in 3.0 that is being fixed in 3.1 due out later this month.

[mguinness]

I'm going to close this PR as I've just created a new repo IdentityManagerUI which targets netcoreapp3.1 that should work for you. It's been implemented as a Razor Class Library that should make integration into existing projects a little easier. I still need to work on README, but the project itself is good to go.