knowledge: fix get_kbr_values returned value

* Fixes the returned value of get_kbr_values:
  list of one element list instead of list of elements.

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>
indexer: PEP8/257 improvements in models

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
records: PEP8/257 improvements in models

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
editor: PEP8/257 improvements in models

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
accounts: enhancement in UserUsergroup

* Adds in the model the update of the date after last change of
  user status.

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>
restful: addition of validate method in RestfulPagination

* Adds a `validate` method in RestfulPagination class that checks
  the ranges of `page` and `per_page` parameters.

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