Avoid handling TurnOverEvent in ball bounce

[IBBoard]

_process_ball_movement() iterates through ball bounce and throw-in events. It also picks up the TurnOver event, but we should be able to identify when it is going to happen before we read it and then let the outer loop (throw, blitz or other even type) handle it so that we're not doing a board.change_turn() in the middle of something else.

[IBBoard]

Removed as part of #4