Mostly cleanup of unused code.
Fixed linespacing to use the font metrics.
Removed unused usings.
Simpler conversion to alpha premultiplied greyscale.
Disabled border padding which is causign artifacts.
Use the font height for unrendered characters.
Initial Xwt Window
Add custom widget for output
More IView
Correct separator in the Menu
Exiting on closing
Beginning UI content
Fix text alignment on output
More IView, plus Handlers
Switching for the Xwt window
Fix filename dialogs to return filename instead of current folder.
Get populating the treeview working correctly.
Updating of controls are invoked to the main thread.
Merge branch 'develop' of https://github.com/mono/MonoGame into thiagoabreu-pipeline-gui

Conflicts:
	Build/Projects/Pipeline.definition
Protobuild definition for MacOS,Linux version of Pipeline tool.
Repurposed PipelineReferences.definition for the Pipeline project.
Previous PipelineReferences.definition is now Framework.Content.Pipeline.References.definition.
Remove unused using statements that caused problems cross-platform.
Moved and added missing file for Xwt project.