WIP
Merge remote-tracking branch 'origin/master' into devtools

Conflicts:
	Perspex.Controls/Panel.cs
Allow binding to plain IObservables.
DevTools now displays the visual tree!
Added a logging manager...

To try and figure out why stuff is flashing up on the screen when you
open a new tree view node, and then decided to put that off for later ;)
No longer need to work around a Splat bug.
Clip controls.

Messes up the treeview item expanded arrows... Probably related to the previous
problem with rendering and rotate transforms.
Display template controls in italic.
Make app into a windows app.

And activate on show.
Lots of changes involving ItemsControls.

Added ItemContainerGenerator mainly...
Fix tree item container generator.
Added a dev tools prompt.