Physic update: Interfaces + move left/right + bugfix 
 * Two new interfaces: IPhysicEventListener, IPhysicSolver
 * PhysicSolver now implements IPhysicSolver
 * GameBoard now implements IPhysicEventListener and use a reference to
a IPhysicSolver instead of a concrete reference to PhysicSolver
 * A IPhysicSolver has a collection of IPhysicEventListener and notifies
them when a physic event occurs.
 * Introduce Enum Direction
 * A IPhysicSolver can now try to move the current brick right or left
 * Lot of bugfixes in physic algorithm
 * GameBoard randomly try to move brick in order to test physic