reworking of the logo, in SVG.

[Dan Haywood]

my 6th idea for a logo, at 
https://cwiki.apache.org/confluence/display/ISIS/LogoIdeas

I'm not sure I like it more than the one we're using (my 1st idea), but 
at least it is in SVG so should be editable/tweakable by everyone (use 
Inkscape as the editor).

Dan