Update the sample

[mlaily]

I wanted to test the feasibility of Razor views in an F# web project, but I realized with this sample that multiple things do not work out of the box.
Since I spent a few hours on this, here are some improvements so others don't have to go through the same thing... :)

Summary of the changes (also see commit list):

• Update to .NET 6.0 and F# 6
• Extract the views to a C# project so we get full VS support in .cshtml files
  • This is probably the most controversial change of this PR. It seems Visual Studio does not completely support cshtml files in fsproj project, and the intellisense does not work. This considerably reduces the usefulness of Razor views.
  • It complexifies the sample a bit, but this seems like a more realistic usage and I think the tradeoff is worth it.
• I didn't check whether Razor runtime compilation properly worked before (it might have been used instead of statically compiled views in release mode too, which is to be avoided), but I made sure it does work now.
• Other minor fixes and improvements.