Added ResumeManager so something can be drawn whilst textures are being reloaded.

*How it works*
The textures are now reloaded on a different thread so execution can continue. The AndroidGameWindow._isResuming is set so the optional IResumeManager can be drawn. A default ResumeManager implementation has been provided so users can easily set it up with a custom texture rotating in the middle of the screen.

*Motivation*
Reloading of textures can take a LONG time. Whilst this occurs the user is presented with a black screen and the music playing. This leads to confusion about whether the game may have crashed. Also, when adding full screen ads to a game, these generally cause the GL context to be lost so when the user dismisses the ad, they are hit with this lengthy texture reload each time.
Convert default ResumeManager to use a ContentManager instead of Texture2D.FromStream
Merge develop3d in resume_manager

Fixed one merge conflict in Adroid csproj
Merge branch 'develop3d' into resume_manager
Merged actual latest develop3d into resume_manager
Merge branch 'develop' into resume_manager

Conflicts:
	MonoGame.Framework/MonoGame.Framework.Android.csproj
Merge branch 'resume_manager' of http://github.com/Aranda/MonoGame into resume_manager

Conflicts:
	MonoGame.Framework/MonoGame.Framework.Android.csproj
Merge branch 'develop' of http://github.com/mono/MonoGame into resume_manager
Updated ThirdParty/Libs submodule to match develop branch
Add RenderTarget2D support

Fix Blender states
Fix Ouya build - add missing files to project
Merge remote-tracking branch 'upstream/develop' into develop

Conflicts:
	MonoGame.Framework/Graphics/RenderTarget2D.cs
Fix usings.
Merge branch 'develop' of http://github.com/mono/MonoGame into resume_manager

Conflicts:
	MonoGame.Framework/MonoGame.Framework.Ouya.csproj
Merge remote-tracking branch 'upstream/develop' into develop

Conflicts:
	MonoGame.Framework/Graphics/RenderTarget2D.cs
BUGFIX: Mipmap levels of DXT textures were not loaded correctly in DirectX.
Merge pull request #1400 from Aranda/resume_manager

Added ResumeManager so something can be drawn whilst textures are reloaded
Merge remote-tracking branch 'upstream/develop' into develop
Remove the RenderTarget2D.cs.orig file
Merge pull request #1427 from jalf/develop

Add RenderTarget2D support