Width, height and numbers of colors in boite json

[vrialland]

Since we now know the kind of display a boite is using, exporting these infos on /boites/<uuid> would be helpful.

Example payload:

{
  "id": 11,
  "width": 32,
  "height": 16,
  "nb_colors": 2, 
  "tiles": [
    {"id": 46, "last_activity": 1529262961}, 
    {"id": 48, "last_activity": 1529262961}
  ]
}