-- Cells now start ticking themselves when activated, and stop ticking
themselves when fully deactivated (no players). More often than not, players only
occupy a relatively few cells at a time. It is rather wasteful to iterate
over all units in all cells in all zones each tick, finding in most cases that nothing
should be done when unit.active is false. These changes make it so that
redundant checks to do not occur. Server start up time appears faster,
but performance gains have not been quantitatively measured.

Signed off by Mark Farrell <markfarr2011@gmail.com>