installation: Flask-Registry version update

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
tags: REST API and testing

* Creates API for tags, in order to have a reusable API
  both for restful API and views probably.

* Refactors tags REST API in order to use the new tag API.

* Tests the tags REST API.

Signed-off-by: Konstantinos Kostis <konstantinos.kostis@cern.ch>