WorldFactInteraction:
Hovering over a worldspace fact in mathmode now shows the fact display. This display can be dragged into scrolls like facts from the fact display.

Additional changes:
- WorldFactInteraction added to Mathmode canvas, as it should only be active if the canvas is active
- Sorting order of Math canvas increased to 10 (from 0), so that dragged facts will always be displayed on top
- DisplayFacts Dictionary is now static and thus available from other classes that need the fact display (this is not ideal and should maybe be extracted)
- DragHandling: dragged variable now public, as this is of interest to other classes