Add brick particle explosion
Put image into atlas
Merge branch 'master' into brick-particle-explosion

* master:
  Set each drop chance to 5%
  Major refactoring of dropping item for extensibility
  Major refactoring of dropping item for extensibility
  change powerupExists flag back to flase if player did not manage to catch the powerup
  ensures no more than 1 powerup at the same time
  adjust powerup starting position to roughly at brick's centre bottom
  uses power_up image file and remove useless console.log statement
  added powerup functionality for extra life

Conflicts:
	public/js/game.js
Merge pull request #57 from nsue/brick-particle-explosion

Brick particle explosion