Get bottom of vertices of the player object

- Get the vertice to get the foot of the player
Maskbit/Colisio/Adding fixture to player

- Adding a body and a foot fixture to the player, make it impossible to
him to "stay fixed" to a wall, while a player push the right key to get
to this wall.
- Making possible the jump only if the foot are touching the ground
- Changing bitmask for the player, making the mist not touching him.
Putting back the wright maskbits to Ery

- Adding one vallue to collider_player to prepare for issue 12
(https://github.com/nanarchrist/Mistery/issues/12)
Pushing for thibault because BEeber is angry
Quedalle à commit
fix jump
change gravity
disable collisions between entities