Added AI Rocket and more music and an endless last level

Using the Unity3D ML-Agents, created an AI controlled rocket that appears after you have complete about 50% of a level. There are two AI brains used, one for the inner sphere and one for the outer sphere which requires more motion as it is a bigger space. the AI rockets are more or less competent players but could be better. There was lots of machine learning experiments and training to get this far. It was and interesting thing to attempt for this game. Hopefully it will allow a single player game to experience a little of what it might be like to play with other players. The last level is now endless. Also, added new a new music set and of course various bug fixes. Hopefully I didn't break anything. Have fun.