Barrel chest

# New Boss Barrel Chest
This closes #52.

Barrel Chest is an dude in a flying suit, kinda like iron man. One catch, he has a gigantic energy canon in his chest. **HIs Chest**!. Oh, another catch: it's the mother flippin' B.F.G.

## Changes to the BFG
Well, not the original BFG. I changed it so that it becomes more of an AOE weapon. The BFG doesn't fire out lines at enemies/rock, instead it will "explode" on impact, sending out shards of energy that deal damage to things around it. It still does massive amounts of damage on contact so it's still okay to call it the BFG.

I made these changes mostly because I couldn't get the lines to look right and also, it was a bit over powered as a weapon.

## Barrel-Chest Attack Strategy
Barrel Chest likes to stay in the air but he tries to keep a close proximity to the player. He flys across the screen and swoops down at the player, pausing every now and then to fire off a blast from his chest-mounted BFG. As Rock deals damage to barrel chest he will attack faster and with more blasts.

## Changes to Game
I re-added the code to pause the game on blur and unpause on focus. I didn't like how the game would run in the background constantly. Also, I completely removed the music. I'll work on replacing this with more manageable file sizes.

you can fight barrel chest with the following setup params: ?level=LevelEnemySoldierTest