Partial manual revert of 168cb146eaec3c568527bbc5dcf06b4cb6e9bda8.
Please note that this does *not* contain any changes to the UI as
discussed; those will follow later.
References #41
Removes obsolete wrench icon; replaces icon-off with icon-logout
and icon-eye with icon-globe or icon-zoom-in; adds icon-cancel as
state indicator for smallscreen navigation.
This includes only the icons actually used or intended to be used
in the backend. Please note that unfortunately, some class names
have changed. Also some icons have been exchanged.