Reworking the collision system.

Probably don't need the Slope/SLOPE classes because we're going to be
using cross product for line intersection. And line intersection will
lead us to object collision.
Reorganize classes/packages.
Line intersection algorithm added.

Based on Andre LeMothe's "Tricks of the Windows Game Programming Gurus".
Cleanup.
Collision detection.

Paddle collision will request for uncached corner coordinates.
Fixes #11. Add ball(center) and brick coordinates.
Add to #11 some debugging.

Save a message to be written out to screen on the next draw()
iteration.
Fixes #9 and a ConcurrentModificationExcpetion.