Update added music.

Added directional music that changed depending on side distances. However, WebGL doesn't appear to support pan stereo and/or issue with my version of Unity. So sadly, no directional music. 

Can select from 5 different songs in 'Esc' menu. 

 Overhauled internal structure from Singleton to Scriptable Objects / Events format. 

Music from: Free - Sci-Fi and Cyberpunk Music Pack | Sci-Fi Ambient | Unity Asset Store