Gcolor2

gcolor2 seems to only load by default the x11 unix palette - i know it's
useful, but interesting would be if we can choose from other palette files
in the same format (gimp and inkscape also use them), like our custom
palettes, and the usual Pantone, Focoltone, etc., for the people used more
these ones.

the palette files could be choosen from a select box in the gui, which the
palette files could be stored in a folder like '~/.gcolor2/palettes'