Feature/json like persistency

Mainly, this PR contains:
* Automatic HiveQL external table creation (it would solve https://github.com/telefonicaid/fiware-connectors/issues/13).
* Json-like persistency (it would solve https://github.com/telefonicaid/fiware-connectors/issues/29).

**[Edit Fermin]** I would say that it partially solves #29, as some things would remaing pending on that issue (e.g. the scripts to convert from old to new format).