-Added new footstep sounds for the Tank.
-Reduced the volume of the Charger's footsteps.
-Added several footstep sounds that were previously missing.
-Change the sounds that play when walking on dirt or grass-type surfaces.

-Changed the survivor's footsteps for the following surface types: tile, concrete, and wood.
-Updated footstep sounds for the Boomer, Charger, Tank, and common infected.

I figured the footsteps noises fit with the physics category better than anything else, so I added it here instead.