Invert the vertical look axis option and balancing

Hello! 

I got some feedback that there should be an option to invert the vertical look axis so I added that.

Also some minor tweaks:

• Adjusted the crawler health so it's a bit less of an bullet sponge than before
• Increased mission area so killing enemies on a wider area count towards the mission objectives
• Enemy car wheel sound is no longer global
• Ammo numbers no longer overlap with the inventory menu