flight velocity integrated into Flight class

Flight:
-now has velocity as its own property
-all references to this.flightplan.getVelocity() -> velocity
-moved constant to convert velocity to pixels to static constant,
gameScale
-added getter/setter for velocity

FlightPlan:
-removed velocity property, getter/setter
-constructor now sets flight's velocity directly
-removed unused variable "int a"

FlightMenu
-all references to flight.flightplan.getVelocity() ->
flight.getVelocity()