Commands even better! But still have oddities

Commands now work, but there are still some oddities. For instance,
sometimes, the units will not follow the player even when they are
selected (but they still accept commands). The "deselect units" code had
to be moved to UnitSelection, then I had to create a new event
UnitSelection.OnDeselect(). Now there probably is no reason to have a
Command.NULL enum item.