Physic: destroy a line when completed
 * modify brick mask
 * update the game board
 * currently does no gravity computation (bricks are floating in the
air) => TODO
Physic: bugfix
 * colliding coordinates where not computed again after brick's mask
modification
Physic: do gravity when line is destroyed
 * PhysicBrick can indicates if it is totally destroyed
 * PhysicSolver maintains a list of Brick which are on the board
Merge branch 'master' of https://github.com/L-Naej/Tetraword.git