[Mac] Remove obsolete methods in Context class
Add some initial infrastructure for the drawing tests
Reorganize test directory structure
Some more testing infrastructure work
Allow saving images
More work on drawing test infrastructure

Added first tests
[Gtk] Partial workaround for embedding an NSView inside a ScrolledWindow

Manually reposition the NSView when the enclosing viewport is scrolled.
Unfortunately, the NSView is still not clipped properly.

This is only meant to be a stopgap until the gtk stack is fixed,
at which point this commit should be reverted.
[WPF] Implement some missing image handling methods
Merge branch 'master' into visual-render

Conflicts:
	Xwt.WPF/Xwt.WPFBackend/ImageViewBackend.cs