setup: better version handling

* Replicates version handling from Flask-Registry. (closes #9)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Better put the same string as in `setup.py`, hence `1.2.0.dev20140812`.

Also note that there is another place with hard-coded version string:
```
workflow/engine.py:__version__ = '1.2.0.dev20140812'
```
We'd better amend this one as part of the same commit.