Add support for drawing halls according to their position define in ipplan.db

[furest]

This PR changes the way the halls are drawn in the dhmap based from the hall_positions in ipplan.db.

ipplan2dhmap.py :

• Also pull the hall positions from ipplan.db and add it to data.json.
• A new "fake hall" named "Position" is added besides "Dist" and "Prod" in data.json

dhmap.js :

• Use a 2D array as a "grid" of halls. Grid cells can be empty and do not have to contain a hall.
• A hall not declared in the "Position" object (c.f. ipplan2dhmap.py) will NOT be drawn
• Support of previous ordering method (based on hall size) has been fully dropped. A hall must have a position in data.json (and by extension, ipplan.db) to be drawn.
• If two halls position conflict with each other (e.g. two halls declared with (x=0; y=0)), the latest defined hall will replace the other.
• Halls are drawn by iterating on the grid cells of the 2D array and drawing it from the X;Y coordinates of the grid cell (as top left corner).