Add better scene switching

[EthanAlmloff]

Switching to a new scene doesn't always work, certain things should be saved which aren't. The actual implementation for this needs some work but for example:

• audio channels
• certain internal systems are removed and re-added that should maintain their state

[EthanAlmloff]

This needs more discussion from more people than just me so I'm removing it from the v0.1 milestone.