The `disconnected_*` boxes are the opposites of the `connect_*` ones,
i.e. when a node has no suitable neighbours on the respective side, the
according disconnected box is drawn.
* disconnected_top
* disconnected_bottom
* disconnected_front
* disconnected_left
* disconnected_back
* disconnected_right
* disconnected (when there is *no* neighbour)
* disconnected_sides (when there are *no* neighbours to the sides)