Airport name made static to make references from other classes easier

boolean flightsOnRunway with getters, setters to constrain number of flights which may take off at once to one
made images static
added buttons to permit a flight to land and take off, with draw, update functions
Booleans holding permission and request to land and take off
Handling of constraints for take off when flight is spawned on airport
Textual alerts when a plane is requesting to land or take off

Removed drawing of flight info in bottom right; replaced with land, take off buttons.
Function to catch if next waypoint is the airport, allowing flight to request to land and begin descent as soon as this is true
Flight only updated if it is not requesting to take off, ie flights on runway will not move until permitted to do so
Allowed flights to spawn on the airport, ie for take off
constraint for only one flight on airport at a time handled - new flights cannot pick the airport if there is a flight on the runway