This way, when the user changes their color theme, any sheets
that did not have a specific color set will change with the theme.
Also add a button to clear color overrides from a sheet, because
any schematics that have been saved before this change will have
the colors set to something other than UNSPECIFIED.
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.