grunt: jquery.hotkeys specify version

* Adds download link for jquery.hotkeys version 0.8 from
  http://invenio-software.org.

* Fixes JS hotkeys conflict in BibEdit. (addresses #1778)

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
installation: requirements update

* Upgrades Jinja version to 2.7.3.

* NOTE Flask-Menu, Flask-Breadcrumbs, Flask-Registry, and Flask-SSO can
  be installed directly from PyPI.

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
assets: filters behavior fix

* Fixes the filters behaviour when no variables are set in the config.

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>
Reported-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>