Added implementation of TextureCube, Texture3D and RenderTargetCube.
Added new the files to all projects. Minor other changes.
Fix to the Mac Gamer services as may of the samples that used it were failing
Merge pull request #1441 from DigitalRune/dxtextures

Added implementation of TextureCube, Texture3D and RenderTargetCube (Windows, DirectX).
Merge pull request #1450 from dellis1972/develop3d

Fix to the Mac Gamer services as may of the samples that used it were failing
Merge remote-tracking branch 'refs/remotes/upstream/develop' into develop

Conflicts:
	MonoGame.Framework/Graphics/RenderTarget2D.cs
	MonoGame.Framework/Graphics/Texture2D.cs
	MonoGame.Framework/MonoGame.Framework.Windows.csproj
	MonoGame.Framework/MonoGame.Framework.WindowsGL.csproj
Oops, duplicate colormasking