installation: addition of OS X installation guide

* Addition of a section on how to install invenio software
  on OS X 10.9 or later.  (PR #2392)

Co-authored-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Signed-off-by: Konstantinos Kostis <konstantinos.kostis@cern.ch>
search: unnecessary `decode('utf-8')` removal

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
legacy: bibrank unicode errors fix

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>