Fixed bug were Texture3D.Format was not set.
Initial implementation of RenderTarget3D for DX.
Disabled RenderTargetBinding to RenderTarget3D for non DX builds.
Added Handle propery to GraphicsDevice.
Merge pull request #1607 from Shqrdx/handle_branch

Handle to Device property for GraphicsDevice.
Merge branch 'develop' into rt3d
Merge pull request #1549 from SickheadGames/rt3d

RenderTarget3D for DirectX
Merge branch 'develop' of https://github.com/mono/MonoGame into develop