checkpoint
Non-building checkpoint in MAJOR refactor.
Added default theme library.
Added some Visual tests.
Added Application library.
Everything compiling now.

But not working, obviously.
Added Diagnostics library.
TabStrip rendering again now at least.
Fixed failing test.
More things rendering, more tests passing...
Things now display correctly.

No keyboard input though.
Make keyboard focus work again.
Removed original monlithic Perspex lib.