Implement color themes (lp:#1678345)
Original report created by Jon Evans (craftyjon)
Users should be able to switch between sets of color options (themes) in
all programs. Ideally these themes should be stored as files that can be
shared / backed up / checked in to source control if desired. Part of this
is a refactoring of the color settings code to be unified among all the
programs, and clean up some aspects of color handling when switching
between legacy and GAL canvases. This will also enable a "reset to default
colors" option, in the form of a "KiCad Default" theme that cannot be
overwritten.