Optimize all SVGs

Passed with svgo 0.4.2 <https://github.com/svg/svgo>, then prepended
'<?xml version="1.0" ?>' prolog back to each file since svgo sees
it fit to remove it and that breaks just about everything.

Skipped the ones in tests/, there's some weird stuff here and they
didn't shrink much when I tried anyway.

Total file size reduced from ~90 KB to ~30 KB, size of some icons was
reduced by 90%.

Change-Id: If05ee0e0ffeadcf5b21e2620cdfeef218e4c0c5d