Created NPC class with basic physics

Also started working on soldier
Forgot to fix soldier frame rate
Projectiles are now killed when they exit level
NPC's given type that will be used for abducting
Weapons can now have unlimited ammo
Score values added to player class
GameScreen now displays gameover text on death
Soldier now randomly picks between male & female
Created Credits Screen & Fixed muzzle flash
SoundHandler now gets passed to screens
Merge remote-tracking branch 'origin/master' into auto-move-files