This is a test OXP which adds a basic multiple-dock carrier to high
planetary orbit, hopefully out of the way of anything important, and
has it launch and recall traders.

Dock 1 is set docking-only, Dock 2 is launch-only, and Docks 3
and 4 are dual-purpose.

Note that it intentionally has a design flaw (the docking corridors
for Docks 1 and 4 are positioned such that ships docking in them will
sometimes block launches from Docks 2 and 3)
