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

Suggested by unity warnings
Old version worked as well

Fact display now also does not cover up the scroll area anymore (mask)
Dragged facts get moved to bottom of canvas hierachy while being dragged, so they are visible above all other ui