List in extended description

Modified health values of easy, medium, and hard ships
Changed structure of submarine to have BaseSubmarine and EasySubmarine
Changed structure of plane to have BaseAircraft and EasyAircraft
Added dummy BaseAircraft and EasyAircraft artwork
Modified test spawn button to cycle through enemies rather than be
random
And added spawning EasyAircraft and EasySubmarines to it
refactored SpawnRandomEnemies in playController to spawnEnemies