WARNING: Expect merge conflicts! This changes a line on nearly every
scene in existence.

However, it clears it all out for the future so we'll never have to deal
with it again.

This prevents hero 1 from permanently setting the objective to one side,
making them very OP and the game un-fun.

Any object with collision mask=2 will no longer collide with the
objective.

In multiplayer, if there is only one hero 1, it is ok, but with more
than one, one hero 1 cannot place walls.