Add project templates for ASP.NET Core 2.0 apps running on .NET Framework

[DamianEdwards]

[mlorbetske]

The 2.0 templates already support passing full framework TFMs via TargetFrameworkOverride (the same mechanism for 1.x) - this option is currently filtered out in the VS UI. Is there more to do here than just not hide them?

[DamianEdwards]

Yes, the templates will require other changes, e.g. the packages referenced.

[mlorbetske]

Partially addressed in #825