Collectible despawn and bullet

Improved the despawning of collectibles, should now be more efficient
Also start adding functionality for bullet
Merge remote-tracking branch 'origin/master'

Conflicts:
	FlappyBird.userprefs
	FlappyBird/FlappyBird.pidb
	FlappyBird/bin/Debug/FlappyBird-unsigned/Application/app.exe
	FlappyBird/bin/Debug/FlappyBird-unsigned/Application/app.exe.mdb
	FlappyBird/obj/Debug/FlappyBird.csproj.FileListAbsolute.txt
	FlappyBird/obj/Debug/app.exe
	FlappyBird/obj/Debug/app.pdb
	FlappyBird/obj/Debug/convertedpdb/app.exe.mdb