Added Music

I fixed a couple small issues, such as part of the exit area being more visible in some levels than others.

Also with the extended deadline, I decided to add music, just simple looping elevator-type track, which I recorded on guitar in Reaper. 

I also realized that I inadvertently kept a feature from my Brownian Motion Simulator, since I started this project with that as a foundation: if you hit Shift you will toggle the NPC visibility. I will leave this in, purely for visual purposes.