Make options page agnostic of session page and implement RangeOverlayManager GUI class, refs #5387, #4747.

Avoids further session commits that missed to keep options.json session code in sync,
enables use of anonymous or object owned config callback handlers and
encourages session developers to make the GUI more reactive to changing options.

Update RangeOverlays when reseting to default, and update
RangeOverlays of selected entities upon closing the page too (not only hotkey).

Differential Revision: https://code.wildfiregames.com/D2389