Implemented the join command, as well as made it so that all units who
are in carriers are set to have moved (so that end turn functionality
does not break)

changed all carrier classes to have a convoyedUnits method which returns
all units convoyed as a list - this clears up special-case issues with
lander units who have two

Speaking of landers, they need deploy functionality in order to choose
which unit to deploy  (right now only deploys one unit)