sqlalchemy: addition of Encrypted column type

* Adds a custom type which is called `Encrypted`. It uses the AES
  algorithm provided by pycrypto in order to encrypt and decrypt.
  (PR #2204)

Co-authored-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Signed-off-by: Konstantinos Kostis <konstantinos.kostis@cern.ch>