2112 - Prepare to accumulate damage

Re-arrange damage_events. Remove redundant time. Combine a and b data under the same sheet. In order to accumulate anything, you need a reset flag. Add a reset flag to source_instances so that accumulated damage can be stored in collision_damage. Fix up enemy_instances and bullets to set the reset flag on spawn and clear on move. Also change behavior slightly so that instances don’t move on first frame spawned (they are at the spawn location.)