[Inkscape-devel] Panel refactoring

I just committed a bit of a larger change with much panel rework.

The main visible changes are with the palettes. In the swatches dialog it will now remember the last palette selected and restore that on startup. In the docked palette at the bottom of the UI it will separately remember the palette used there (not quite per- document yet).

The docked palette will also now shrink when it's "Wrap" menu item is unchecked. It respects the selected size, and places only a single row. In hand with this and the remembering the last palette, someone can probably now change the default preferences to use a small size, turn off wrap, and select the "SVG" palette. Then have the palette shown in the UI by default.