Merge pull request #1 from pau-minoves/feature/random-movement

Feature/random movement
a bit of renaming
Secured some framework methods:
* Game.getEntity
* Game.removeEntity
a bit of renaming
[BUGFIX]Fixed bug when adding entities to the Game. Only the first
Entity of each Kind was really attached to the AndEngine. The following
were ommitted.
* removed Goals from the field
* added new sprite for the LaserBeam (lacks alpha channel)
increased sprite sizes to 100px
refactor in LaserBeam:
* remove Ball related methods
* added Laser related methods (still work in progress)
updated Laser sprite, now with alpha channel
(next step should be rotating the laser)
Multi commit:
* cleaning of old /gfx
* LaserBeams rotate to target
* LaserBeams go to Infinite by default
* LaserBeams are removed from game when out-of-screen
* small renaming
* added StormTrooper (test sprites)