installation: version generation change

* Changes the version generation to be more dynamic - using Git
  information (same technique as Invenio).

* Bumped the main version to 2.0.1.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
fabfile: add Celery restart step

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>