Added support for /copy items. Xna project items with no processor or importer specified are imported as copy items.
Whether an item is copied or built can be set by via ContentItem.BuildAction (visible in the property grid).
PipelineProject / ContentItem now hold onto the IController rather than the IView (not totally sure which design makes the most sense).
Added IController / IView callbacks so that the treeview can update a node based on dynamic property values.
Merge branch 'develop' of https://github.com/mono/MonoGame into PipelineTool
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
Merge branch 'develop' of http://github.com/mono/MonoGame into develop