Major changes. projectiles and background loop

+projectileManager.cpp :
ADDED: our ship now shoots lazorz :3 (and its even properly positioned)
+ level.cpp
ADDED: class that handles level(s) was added to the project, however it
will require some changes in the future for sure.
+ projectiles spritesheet, space background spritesheet
Merge remote-tracking branch 'origin/Artur'