oauth2server: fix support of SQLAlchemy-Utils

* Addreses issue with new API of EncryptedType in
  SQLAlchemy-Utils>=0.28.2.  (closes #2629)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
installation: python-twitter>=2.0

* Updates python-twitter in requirements.txt to the latest version
  (2.0) that supports Twitter 1.1 API.  (PR #2015)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>