Delete Render buffers for each Render Target binding in SetRenderTargets when the render target is passed as null which signifies resetting the Render Target bindings.
Merge pull request #1472 from kjpou1/develop

develop - Cleanup Frame Render buffers for RenderTargets
Take out check for GL Error on FrambufferRenderbuffer commands in SetRenderTargets.
Merge pull request #1477 from kjpou1/develop

develop - Take out check for GL Error on FrambufferRenderbuffer commands in SetRenderTargets
updating Timer system
Merge remote-tracking branch 'remotes/upstream/develop' into develop3d

Conflicts:
	MonoGame.Framework/Graphics/GraphicsDevice.cs