Review and update dependencies in vsixmanifest

[rynowak]

https://github.com/aspnet/Razor/blob/master/tooling/Microsoft.VisualStudio.RazorExtension/source.extension.vsixmanifest#L16

Many of these still say 15.0 even though we're targeting 16. The MPF one in particular may cause issues.

[rynowak]

Fixed: dotnet/razor#42