Replace image icons by font-awesome, refs #967

Replaced in most of the places, but not all. Added helpers for all icons being
used, but some views are still including the images directly.

Also removed several icon images that are not being used anymore.
Fix error on .visible-on-hover

Was binding to the wrong event on jQuery. Error introduced by bd94de9e3d.
Remove includes to fcbkcomplete on events

fcbkcomplete was removed I while ago, /events/index was failing to load because
of it.
Fix layout for active tab no private messages

Wasn't selecting the appropriate element so the menu item didn't get selected.
Update the small logo and favicon to Mconf's "new" logo

Also update the layouts to use the helper `favicon_link_tag` and moved
some source images to assets/images/src.