Added vortex flight.

Now spawns facing you again. Longflight is disabled for fast-return
protocol. Longflight is now a toggle in the interior rather than an
admin-set option. E2 commands added for longflight and materialising
from longflight. Vortex flight basically allows you to dematerialise
without setting a location to reappear, then you can either set that
position mid-flight using the skycam or typewriter or just rematerialise
in the place you took off from. These changes also apply to regular
longflight, so you can change your mind about the destination whenever
you're in the vortex. To activate vortex flight, press the
'Dematerialisation Circuit' and then the throttle (in simple mode) or
the usual for advanced. Also bug fixes and various small changes.