This drops .NET 2.0, 3.0 and 3.5 as as supported .NET runtime platform.
The maximum version can only be v4.0, which targets currently all .NET
4.x releases. Therefor I added the sku flag to enforce .NET 4.6 as
minimum runtime platform. Since .NET 4.x is backwards compatible we
should be safe to only set the minimum version/sku here (i.e. we should
be able to run the application on a system with .NET 4.7)
refs #7090