Big update to taxi computers and calling.

Fixed taxi movement and hyperspace issues I was having.
Made taxi computers more modular, because there was a lot of repeated code.
All stations now have taxi caller buttons with taxi access.
Taxi computers now only list the living stations unless they get emagged, then they also list the derelict.
Taxi buttons at derelict don't work. Honk.
Forgot taxi buttons and edited how the calling system works.
Merge pull request #1802 from ComicIronic/NuTaxi

TAXISTATION: Update to taxi movement