cloudconnector: improvements and fixes

* Several PEP257 and PEP8 fixes.

* Deletes `factory.py`.

* Creates `utils.py`, `registry.py` and `manager.py`.

* Uploads a file to a cloud application.

* Uses `refresh_token` to get a new token when the token is expired.

* Adds SQLAlchemy signal 'after_insert'.

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>