Okay okay. Lots of changes here. I primarily took care of this
first implementation of Collision in response to Billy's implementaion
of collision detection, and Dalen helped with the
display.py fix - in fact, I'd go as far as to say that Dalen pretty much
dictacted the entire fix while I just wrote the code.

Okay, so here are the changes:

display.py
we changed the print(Cell.color) to just print "", to avoid printing out
each cell's color at every tick.
For some reason, when the print function is removed entirely, the program
runs extremely slowly. It seems that there's some bug in display which
requires the print statement as a sort of Duct-tape fix... macgyver style...
Dalen was pretty much entirely responsible for this
TODO: Fix taht

cells.py
I did this pretty much alone, though Dalen helped fix some syntax errors I
made in the initial writing.
Billy's initial implementation of Collision detection was really inefficient,
because each cell went through the list each tick. Now environment handles it
the collision-detection instead, which works fine.

environment.py
Collision detection is here. Right now, when cells collide, they lose all
velocity and acceleration.
TODO: delete the extraneous Tick function which appears before the
SECOND tick function. Also, implement the actual collision.