Health indicator

I pulled the work @WGrube28 did on the health indicators over and cleaned them up a bit. Now the player has a blue health indicator and the spider tank has a black health indicator. I also removed the existing UI stuff since it's no longer necessary. I think we should still have a health display for the boss that's part of the UI, but having one that follows the boss might also be a good idea because the player won't need to look away from the battle to see how much health the boss has.