Fix a bug happening when the robot enter in a new cell

When the robot enter in a new cell, he updates the back wall to NO_WALL,
but to do that he have to use the relative values of the position, not
the position on the map. This terrible mistake made the robot bug in the
negative cells.
Change priority of ColorMaintainer to stay with RM

(+ order tasks by priority)
Fix 2nd bug : wrong negative cells
Merge branch 'developer' of https://github.com/Oroles/MazeSolver into reinitialize_position
Split the read distance task in 3 different tasks