adding icons in gaia shared folder, and updating templates

@wilsonpage could you test that on gallery app to see if we need any extra fine-tune?
You should probably need to add class ´gaia-icon´ next to ´icon-... ´
If we use ´[class^="icon-"]:before, [class*=" icon-"]:before´ selectors, we will be applying the new icons to places in gaia they are still not ready to migrate to gaia-icons :)