Added Airport class which extends Waypoint (currently placeholder image)

Added an instance of Airport to Demo

all tests pass
Increased the radius of waypoints for picking up changes in flight plan
started preparing to add functionality to airport, now acts as a normal
entry or exit point.

added to drawMap() in demo, now you can view flightplans by just mousing
over planes, selections still made by clicking.

Test for waypoint was failing because of increase in acceptable mouse
radius, test is changed accordingly.
Changed the placeholder image to a green circle, changed the reference
in airport to the correct image
Small cleanup
Airport will only appear as an exit or entry point, 

all tests ran fine.

Branch complete yo!
Merge branch 'Airport' of https://github.com/liam-m/SEPR-MQV-2.git into
Airport

Conflicts:
	BTC/src/scn/Demo.java
Merge remote-tracking branch 'origin/Airport'