introduce Map.disjoint, Map.set_disjoint and Set.disjoint

or unknown can be seen as valid...

rename location_color to goal_color and lighter_location_color
to premise_color

defaults are "yellow" and "gold" and if you don't like them change them

are not the actual goal.

It's still madness. We shouldn't open our quantifiers every time
we redraw screen. This needs to be fixed.