UI should accept keyboard input

[knowknowledge]

The UI Widget needs to have a way to handle keyboard presses. Each container Widget needs to be able to send key events to specific focused children.

Example uses:
Typing text in textboxes.
Tab to move between focused boxes.
Escape to close windows.
Enter to accept an accept button.

[chris]

I'm literally implementing this right now (12/26). It should appear in my UI branch on github around 12/28.

[knowknowledge]

The Textbox has been partially implemented at this point.

The Window does not yet capture Tab, Escape, and Enter keys.

Moving this to 0.3.0 development.