Added Gtk to VS/windows solutions

Windows and Linux seem to be arguing about line endings on .gitignore
and packages.config...
Make TestApplication use Win32/D2D again.
WIP refactoring Window.

To make it x-platform. Currently breaks input.
Handle input again.
Prevent timer delegate being GCd.
Handle window resize.
Make Perspex.Cairo compile again.
Initial implementation of gtk WindowImpl.
Getting something drawn now.