Feature dock area

This is an initial cut at a visual-studio-like docking framework which goes far beyond the capabilities of the standard Qt docking framework.

Highlighted Features:
* Unlimited dock split nesting
* Intuitive docking guides
* Full save/restore capability
* No central-widget requirement

To-be-implemented Features:
* Floating dock areas
* Title bar icons
* Snappable floating windows
* Auto-hide toolbars