installation: SQLAlchemy, SQLAlchemy-Utils upgrade

* Updates minimum and maximum version requirements for
  SQLAlchemy and SQLAlchemy-Utils.  (closes #1776)

* Fixes compatibility problems with SQLAlchemy>=0.9 version.

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>
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>
workflows: harvesting description arXiv link

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
workflows: blocks in styles templates

* Adds blocks and base template for workflow styles templates.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
workflows: attached files improvement

* Amends a bit how the "files" task result integrates to show
  any uploaded files in Holding Pen detailed view.

Co-authored-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
workflows: styles fixes

Signed-off-by: Georgios Papoutsakis <georgios.papoutsakis@cern.ch>
workflows: error signal catching
workflows: indentation from 4 to 2 spaces

* Updates indentation from 4 to 2 spaces across all templates in
  the module.

Reported-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
general: importing modules from packages fix

* Uses Flask-Registry for importing modules from packages.

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
previewer: pdfjs plugin addition

* Adds pdfjs previewer.

Signed-off-by: Adrian Pawel Baran <adrian.pawel.baran@cern.ch>