Ensure foreground context is current on the main thread

Background must be non-current, otherwise it will raise error 170
(resource is in use) on the next MakeCurrent() call.
Merge pull request #2476 from SickheadGames/PipelineTool

PipelineTool import fixes
Merge pull request #2477 from thefiddler/fix2474

Ensure foreground context is current on the main thread
Removing assert Pow2 from Texture.GetPitch. It is not appropriate to have this assert in the base Texture.cs file because it is platform specific whether or not this is actually a valid constraint and area already doing their own dimension validation.
Merge branch 'develop' of https://github.com/SickheadGames/MonoGame into develop
Merge branch 'develop' into PipelineTool