[wip] [avar2] Redesign designspace navigation panel, rework internal font location vs glyph location

[justvanrossum]

• Redesign the designspace navigation panel to clearly separate font axes from glyph axes
• Use new ui-accordion web component, so we have three collapsable sections:
  • font axes
  • glyph axes
  • glyph sources

Todo:

• [ ] fix interpolation errors section styling
• [ ] internally separate font location vs glyph location
• [ ] hook up the glyph axes
• [ ] ...