Use popovers for advanced tool settings in header

[jlampel]

Some tools, like Relax, have a ton of options that can be tweaked that don't fit in the 3D View header. In those cases, we should use popover panels to still expose them while saving space. The current sections that should be moved into popovers in the header are:

• Algorithm (Relax)
• Masking (Tweak, Relax)
• Tweak (PolyPen, Strokes)

[jlampel]

Note: When I do this, I should be sure to include Blender's auto-merge distance in the Tweak popover.

[jlampel]

This is in, but I'd like a quick review from @vxlcoder before considering it finished.

Main question:

I'm registering all the panels separately in RFCore, which looks a bit messy. Is this something I could do with RFRegisterClass? I poked around the registering system a bit but tbh I don't fully understand how it's finding and registering all the subclasses. Or is it fine as-is?

[vxlcoder]

will take a look after the refactor is complete!