Add function all_cells_visited

The purpose of this function is to check if all the cells are visited, so it can stop if there nothing more to visited. Later will be add a function which finds the first unvisited cell
Rename method all_cells_visited

Now the method it's called find_unvisited_node and returns a NULL if there isn't an visited cell. Otherwise returns a pointer to node cell.!!! User it's responsible to delete the pointer!!! otherwise MEMORY_LEAK
Merge branch 'developer' of https://github.com/Oroles/MazeSolver into mapping
Merge branch 'developer' of https://github.com/Oroles/MazeSolver into mapping
Take in consideration unvisited cell

Now when all the neigbours are visited, it checks for the closest unvisited cell, and will return the direction of the next cell, to reach the unvisited cell.
Modify the alg to find next cell

now I also cover the case in which there is no unvisite cell, this case should never happen but anyway
Resolve bug

In case that in the negative x or y was a free cell it didn't worked, now is working.
Calibration of wheels and wheelbase

It works !!!!
Fix the move_forward for negative values
Merge branch 'developer' of https://github.com/Oroles/MazeSolver into developer