Blender Git Loki

UI: Re-arrange Overlays popover

Organize content in categories/sub-panels.

The result is a more organized but slightly taller popover.
Once sub-panels are implemented code-wise, the alignment issues
(like panel label) and extra space between the content and panels
headers will be reduced. Together with the ability to have certain
less-used popovers collapsed by default, this will make the
popover more compact.

Part of design: T55863