Fix GraphicsDevice.SetRenderTarget and GraphicsDevice.SetRenderTargets on PlayStation Mobile.
Merge pull request #1605 from kevingadd/psm_fix_rendertargets

Fix RenderTarget2D on PlayStation Mobile
Initial check in of Core "Split" Project

* Windows Project implementation only
* Added PCL Targets Foder with PCL target libs and instructions
* All files unchanged except for:
  -  additional #if statements for core project
  -  patch to Content/ContentTypeReaderManager.cs to allow for core type resolution
* Single solution files for Windows VS and Xamarin Studio
Merge branch 'developcore' of https://github.com/DDReaper/MonoGame into developcore
Merge branch 'develop' of https://github.com/mono/MonoGame into developcore
Reverting files back to develop originals