add muzzle flash animation while shooting
fix player death bug and add enemy healthbar

* fix an error that coul make the player invulnerable if it's hp is below 0
* add a statusbar for the enemies health
Fix bugs and implement weapon change with item

* fix muzzle flash bug for single shot weapons (like Pistols)
* implement functionality to change to new weapon by collecting the item
* move weapon stuff from main to player class