linkbacks: fix tab visibility if excluded

* Adds module to excluded packages and disables tab in detailed record
  view.  (closes #1707)

* NOTE Adds deprecation warning for linkbacks module.

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
The default is `0` in `invenio.base.config` for legacy purposes. If you enable module we enable also the legacy code.