revert changes for ajax_resync_favs

see #105
support for resync-parameters
- the css-selector for the resync-buttons changed from id to class
because we can have multiple buttons for the same mod
- add a optionally data-resync="{type:'favs'}" - attribute to a button.
the value must be a valid json-string, it is interpreted by the browsers
eval-function
- these values come back to ajax_resync_items as POST-parameters and can
be interpreted there