[Dextrose] [DESIGN] backport spiral and color picker from 0.90

[Bernie Innocenti]

These two features look cool in screenshots and are relatively safe to
backport.

Sounds lame? The intent here is giving Dextrose 2 a distinctive visual
change compared to the previous version. Users tend to notice visual
changes, especially in our target age.

For the same reason, we should change the logo colors on every release.
Perhaps Dextrose 2 should have the Uruguayan colors?

-- 
   // Bernie Innocenti - http://codewiz.org/
 \X/  Sugar Labs       - http://sugarlabs.org/