After a lot of work, the collisions between the player and the objects are done. The system is more complex that the previous system, greatly because the objects have a finite size and a finite tickness (whereas the walls have an "infinite" tickness).
So i had to find a way to make those collisions the better possible.

In order to facilitate the work, each block is divided in 25 smaller blocks. It's those small blocks that will serve as a mark for the collisions. In one small block, there can only be one object. The collisions are in that way simplified and i can have only one type of collision for all the objects of the game.
The constraint is that an object can't be bigger that a small block, but it's not really a problem in fact.

Here comes a short video that illustrates the collisions between the player and the objects: