Moved FactScreen to top right corner
Default visibility is off
Only for Desktop UI (not Android) right now

Added a SoundManager Class and a Volume Slider to the options menu that can be used to change the volume of all sounds.

The toggle button will be used to filter for favorited facts

Facts can be marked as favorite on middle mouse button click.
Favorised facts are indicaded by a yellow star in the top right corner.
Other fact displays will be updated accordingly and newly spawned fact displays will show the favorite star correctly.

Additional changes:
- Refactored Prefabs/UI/Facts project structure

Implemented UILine

Parent facts are connected to the main fact by a direct dashed line whereas child facts are connected by a jagged continuous line.

The FactExplorer Window shows other facts that reference the selected facts and also shows facts referenced by the selected fact.

Additional changes:
- reverted SortingOrder of MathMenue Canvas back to 0 (was 10)