sqlalchemy: fix mysql index creation

* Fixes checking of Text type supporting the case of NullType
  column type.

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>
groups: port missing functionality

* Adds implementation of user group manage function.

* Adds filter on list of group that user can join.
  (closes #1788)

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>
setup: WTForms pin version 1.0.5

* NOTE Invenio installation is currently broken. Flask-Admin does
  not support WTForms>2.0.0. This is a temporary commit until it is
  fixed.

Signed-off-by: Javier Martin Montull <javier.martin.montull@cern.ch>
knowledge: API migration to SQLAlchemy

* Replaces run_sql queries with SQLAchemy query.

* Refactors module in order to move logic from api to model.

* Fixes bibknowledge webinterface kb mapping update.

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>