Add Remora.Sdk.Web and Remora.Sdk.Razor

[TheBrambleShark]

Adds two new SDKs: Remora.Sdk.Web (backed by Microsoft.NET.Sdk.Web) and Remora.Sdk.Razor (backed by Microsoft.NET.Sdk.Razor).

Both are pretty much identical, except for which Microsoft SDK they import.

Fixes #16

TODO:

• Create AspNetCore Web App (Razor) Test Library
• Create Blazor Server Test Library
• Create Blazor WASM Test Library (Uses Microsoft.NET.Sdk.BlazorWebAssembly)
• Create Razor Class Library

[TheBrambleShark]

I may need to change my approach here. Seems there are many more SDKs that we may want to support, like Microsoft.NET.Sdk.BlazorWebAssembly

What I may do here is instead create a Remora.Sdk.Common that doesn't create its own package, but provides a base for all libraries extending the base Remora.Sdk. Then these extended libraries should be fairly straight forward - the .msbuildproj should just declare variables and then import the .Common SDK. Only thing I think it may have is the packages props for solution packages, but I'm not entirely sure where to handle project packages unless that's also done in the msbuildproj.

Feedback is welcome.