Add 256x256 and 64x64 Beremiz icons


remove svg:midPointStop tags from icons.svg, because Inkscape
complained about unsupported tag. It seems that these tags were made
by Adobe Illustrator and aren't supported by any other app.

<?xml version="1.0" encoding="UTF-8"?>
<BeremizRoot>
  <TargetType>
    <Xenomai/>
  </TargetType>
</BeremizRoot>