#221, #242: Fix/work-around for AI traffic issues

#221, #242: Fix/work-around for AI traffic issues
Move the disable-HOT feature from the MP aircraft to the a/c base class,
disable HOT for all AIaircraft, since that's a fix/work-around for
#242: AI aircraft respect the user a/c only when HOT is _disabled_ for them
#221: AI aircraft don't stack at parking positions when HOT is disabled
Also generally disables HOT for ballistic and other models (suggested by vivian),
allowing it for ship/carrier models only.