GetBackBufferData implementation for OpenGL (Others are just stubs currently).

Docs:
http://msdn.microsoft.com/en-us/library/ff434115.aspx
http://stackoverflow.com/questions/1352864/how-to-get-uiimage-from-eaglview/1945733

refs #1885
DirectX implementation of PlatformGetBackBufferData
Tidy up OpenGL implementation of PlatformGetBackBufferData to match and comment the public function
Fix GL.ReadPixels call for IOS
More comments on pixel formats by platform
Support non byte[] for GL GetBackBufferData (Thanks @thefiddler)
GetBackBufferData Windows Phone support
Fix build on MonoMac
Initial Xwt Window
Add custom widget for output
More IView
Correct separator in the Menu
Exiting on closing
Beginning UI content
Fix text alignment on output
More IView, plus Handlers
Switching for the Xwt window
Fix filename dialogs to return filename instead of current folder.
Get populating the treeview working correctly.
Updating of controls are invoked to the main thread.
Merge branch 'develop' of https://github.com/mono/MonoGame into thiagoabreu-pipeline-gui

Conflicts:
	Build/Projects/Pipeline.definition
Protobuild definition for MacOS,Linux version of Pipeline tool.