For convenience, move icon sets out of `iconset` folder and include core-icon in each.
Add editor icon set

Refresh icons from assets
Add GitHub to social icon set
use svgo to optimize github icon
update icons
Merge remote-tracking branch 'Polymer/master'

Conflicts:
	communication-icons.html
	core-icons.html
	device-icons.html
	editor-icons.html
	hardware-icons.html
	image-icons.html
	notification-icons.html