sqlalchemy: refactoring and addition of Encrypted Type

* Addition of package `types` inside ext.sqlalchemy package.

* Refactoring the current types by removing the `types.py` file
  and adding each type to separate file.

* Addition of a type named `EncryptedType` that will be used for
  encrypting and decrypting access_tokens.

* Renames the `EncryptedType` class to `Encrypted`.

* Refactors the class by adding private functions for encryption
  and decryption.

* Adds the `Encrypted` class to the types init file.

* Addition of pycrypto(version 2.6.1) to `setup.py`.

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