Make gui/teleport respect mounted units, better categorize tame megabeasts

[Bumber64]

gui/teleport will teleport merchants off of wagons if the wagon isn't set to be teleported. The merchant will teleport back to the wagon the next game tick. The utility should either dismount them or refuse to teleport them instead.

Tame megabeasts get selected along with hostile units. They should probably be categorized as friendly? (It probably wouldn't hurt to categorize the fort's tame animals as citizens, separating them from merchants and their haulers.)