The swatches are surrounded by non-scaling icons. We should not scale
the swatches unless we also scale the icons. This patch makes all
elements in the appearance panel equally non-scaling
This relates to https://gitlab.com/kicad/code/kicad/-/issues/11880
Rather than detaching and re-attaching the layer panels with the
attendant overhead, we keep each panel intact and only update its
contents. Since the bindings are the same, this saves substantial time
on pcb loading as well as when closing the board setup dialog
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.
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.