Alpha boss

Implements the new boss behavior for the alpha build. In short:

- The boss starts outside the arena and waits for the player to kill all of the minions before entering.
- The boss will leave and heal up once a certain amount of damage has been done to it. It will re-enter the arena after all the minions have been killed or it reaches full health.
- While in the arena it will semi-randomly switch between the basic state, the turbo state, and the laser spin state.
- While fleeing/entering the arena minions spawn to draw the player away from the boss and prevent them from taking it down too quickly.

This is only setup on the `Basic Boss` scene, it hasn't been fully brought over to the integrated level.