Check in of Single solution projects - from develop branch onlu, no changes reqd

* vs solution - MonoGame.Framework.sln - Manages all windows based solutons

* Xmarin solution - MonoGame.Framework.Xamarin.sln - Manages all solutions supported by Xamaring Studio (Needs Trial or Ent license to build)
Merge branch 'develop' into develop.singlesolution
Merge pull request #1639 from DDReaper/develop.singlesolution

Check in of Single solution projects
Merge branch 'develop' into develop.portable