Blender Git Loki

Cleanup SVG icons file: pass I.

Made sure each icon has its own, 'private' group.
Removed empty groups, and some stray paths and rects (among other benefits,
'make icons' do not generate anymore that half o dozen of empty icons one had to remove
by hand before committing ;) ).

Note: double checked, only five generated icons differ (on binary level) from before,
with no actual visual diff.