Ignore space taken up by ammo clips for rearming craft

Determine number of clips reserved for the craft and ignore their space
when calculating the base's used storage.  This will allow player to
juggle craftweaponry without triggering a stores overfill.
Add transfered craft's inventory size to base's
Add transfer craft's inventory to sellscreen when stores overfull
Fix rounding error
Block craft transfer if not enough storage for its inventory