Needed: Battle animation callbacks

[jonoxia]

• callback for start-battle animation
• callbacks for individual attack animations
• monster death animations?
• figure out how to handle the timing of all these animations, i.e. pausing the main battle loop until each animation is done

[jonoxia]

For the timing issue, maybe a BatCmd execute method should return an animation, and the battleSystem runs the animation and pauses the turn sequence until the animation's done?

BattleSystem's animator currently does battleSystem.draw() at the end of each frame because the logic is copied from mapScreen. But if we're going to be drawing SFX to the screen (fireballs, sword slashes, etc), those need to be drawn after battleSystem.draw() draws the background.

Each frame of animation, the following needs to happen in this order:

• draw the background
• draw the monsters
• draw any special effects
• draw any menus