deposit: datetime picker library modification

* Changes the datetime picker library from the jQuery UI to
  bootstrap-datetimepicker.

* Increases the consistency with the Bootstrap design.

* NOTE introduces new JS library
  <https://github.com/Eonasdan/bootstrap-datetimepicker>.

Signed-off-by: Pedro Gaudêncio <pedro.gaudencio@cern.ch>
Co-authored-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>
Co-authored-by: Javier Martin Montull <javier.martin.montull@cern.ch>
oauth2server: fix token expiration and refresh

* Sets access tokens to expire after a given time interval.

* Ensures only confidential clients can refresh an expired access token.

* Adds tests for token expiry to ensure correct behavior. (closes #2112)

Co-authored-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>