Updated Box2D.

Updated to use Box2D 2.2.1 built from a custom Portfile so I could
use the same code on MacOS and Linux.
Delete dead code. Use antialiasing for lines.

Removed the old, commented SDL drawing code. Also use antialiasing
to draw the box borders.
Changed screen size to 1280x960.
Remove SDL drawing code.
Added a reset command.

Made the 'r' key reset the world, clearing all boxes and user-drawn
walls.
Removed 'colorboxes' from git ignore file.

On Mac OS X's case-insensitive file system, this entry was causing
problems when trying to add files in the ColorBoxes directory.