More Pushback options#349

Due to the complexity of some airports, custom pushback options for those should be added as well as optional release points for some.

Examples:
In Zurich, aircrafts parked on the A/B stands on taxiway N may push back facing North on Foxtrot in order for inbound aircraft to be able to taxi to their stand without much delay. - “Swiss XYZ, pushback approved facing north on Foxtrot”

In Frankfurt, set pushback areas are used and are marked on the ground.
“Lufthansa XYZ, pushback approved, Area 4”

In Amsterdam, most stands have a standard pushback, also marked on the ground, so no specification of direction is needed. “KLM XYZ, pushback approved.”

On other airports, you may want aircraft to extend or shorten their push, so you want them to release the push abeam another stand. “Plane XYZ, pushback approved facing North, release abeam Stand XYZ.”

On some airports, like Munich, you have different Taxi Lines (Blue, Center, Orange), so ATC might ask you to push onto the Blue line instead of the standard pushback onto the closest line to you (the Orange in this case.) “Lufthansa XYZ, pushback approved facing West on the Blue Line.”