Need to be able to reorder components

This is quite important for complex glyphs, as is common in CJK design.

Relates to #1117.

Visually this could be a list with an item per component, where each item shows the whole glyph and the component highlighter. Reorder by drag and drop seems like an obvious choice.

Start by locating the glyph component editor and read the related issue #1117 for context. Define the component list and drag-and-drop interaction described here; done means components can be displayed, reordered, and the resulting order is retained in the glyph.

Written by the indexing model from the issue text.