Add Shuttle Transit to Mining and Research Shuttles, remove redundant sprite

- The Mining and Research Shuttles now both go through a shuttle transit zone, much like the pods and emergency shuttle. You now need to buckle on depart and arrival, the pod door closes and locks during transit (air CAN be sucked out) and opens and unlocks on arrival
- Code of both shuttles cleaned up (they're copypaste otherwise)
- Transit time is now 30 seconds. 10 seconds to depart (unchanged) and 20 seconds on the move (added)
- Attempting to remove redundant sprite used for external shuttle corners exposed to space

Known problems : 

- Said redundant sprite removal breaks when the shuttle moves (includes the shuttles and pods). This is only graphical but extremely jarring. To be exact, the wall corner no longer has an included 'space under the wall' sprite and uses transparency. Ideally this would work without a single hitch since there is ALWAYS space under the pod in theory, but when moved the system goes full retard and the space tile under it is deleted, leading to a black background. This only affects the shuttle itself and doesn't seem to corrupt other tiles, or immobile shuttles such as the Arrivals one

I'm pulling in this state since this problem isn't critical and most likely can someone with some smarts figure out a decent fix. Otherwise we can either do with it (the original 'space under wall' sprite looks even worse off during transit even though it works normally) or I can revert THAT change partially