Be more intelligent about sorting lib tree items. (Footprint
entries, for instance, come out of an already-sorted list.)
Don't recreate menus twice when laoding Footprint Editor.
More pervasive use of WX_FILENAME to avoid expensive calls to
wxFileName::SplitPath() and string concatenation.
For POSIX kernels do all the work on the file-system side so we
don't have to keep converting back and forth between encodings.
This introduces COLOR_SWATCH, which is a reusable
widget that shows a color swatch and can invoke the colour picker
when duble/middle clicked.
It uses it's own wxCommandEvent to signal the change.
This makes the layer widget simpler internally, and also allows other
code to show identical swatches if needed.