Limited locker capacity

Mobs now requires 15 units of storage in a locker to fit. Allows two mobs in a single typical locker as they have a capacity of 30, assuming there are no other items inside.

Items take up (w_class / 2) rounded up capacity. Any higher, like a straight w_class, and many lockers cannot fit the items they originally contain. 

Also includes minor sound-play cleanup.