The context menus for items and folders are now defined in the WinForms designer.
Reusing the existing add/remove item logic in the context menus.
Added per-item build/rebuild/clean options.
Further context menu cleanup.
We can now save temporary partial projects.
Added support for rebuilding individual content items.
Merge pull request #2643 from SickheadGames/pipeline6

Pipeline Tool Item Rebuilds