Some small fixes

Hey! Just a few things, for now:

• The fixed machine gun turrets caliber has been corrected. The Cal. 50 was a little misleading, cause they're good but not THAT powerful. It's now 7.62x54r, makes more sense.
  
• And always the fixed machine gun turrets do a little more damage, now
  
• The Zombie Big Soulless (the enemy that charges you) is now less bullet spongy
  
• Fixed some levels colliders here and there