connector: code separation from __init__

* Moves package `__init__.py` to `connector.py` to pave the way for new
  REST API client code.  (closes #6)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Invenio Client v0.1.0

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