Physic: line completion detection
 * physic module now detects when a line is completed
 * physic module notifies its listener when a line is completed
 * Currently the line is not destroyed, TO DO
 * Introduce the interface IBrickFactory
 * BrickFactory implements IBrickFactory
 * DebugBrickFactory implements IBrickFactory. It is used to set in
advance the sequence of bricks we want, in order to debug the game.
 * Minor stuff