SVG font dialog face-lift

Merged Mike Kowalski requested to merge mkov/inkscape:fontdlg into master

Project to prettify SVG font dialog, fix nagging selection issue and let dialog be narrow.

  1. Font list moved to "Global settings"
  2. Fixed font selection that's been constantly cleared by needless dialog updates
  3. Selecting first font on resource change to make dialog instantly usable (enabled)
  4. Removed hard-coded sizes for lists and previews
  5. Reduced minimal width of the dialog
  6. Modified layout of global settings by lining up widgets in a grid
  7. Changed preview color to use theme foreground (no more black glyphs on a dark background)
  8. Adjusted margins and label casing