Fixed block spawning bug.

Raised the height at which new blocks spawn on the board. This fixes two
bugs: (1) when the board is overflowing, the last piece no longer
visibly spawns above an existing piece; and (2) blank opponent boards no
longer show an incorrect block at the top of the board.
Added house-keeping of OppControllers when leaving the board page.

Also removed some unneeded print statements.