Big flight path generator + constants refactor / rewrite

I'm putting this here since I can't see many people around in the labs at the moment.

These load of commits:
* Replace Waypoint with FlightPlan - this means speeds and altitudes are no longer stored with each waypoint. Only the flightplan's initial speed + altitude are stored.
* Merge DefaultFlightPathGenerator and DefaultObjectCreationRate into a new FlightPathGenerator class.
* Added maximum number of flights
* Flights will not enter at an entry point which already has an aircraft near it (should stop some of the impossible to avoid collisions)
* Moved lots of the game constants (most were in FlightPathGenerator) into a new Constants class
* Expanded the Utils class and moved it into the logic (so there are no circular dependencies)

Does anyone particularly dislike the way I've done this?
Unless anyone says anything, I'll merge this tonight / tomorrow at some point.