Doesn't work after install due to configuration handling issue

[osma]

After installing Annif using python setup.py install (within a pipenv shell) I cannot run Annif anymore but get this error message:

ImportError: No module named 'config'

The problem is that config.py is not included in the installed package. It could probably be overridden using an environment variable, but there should be a sane default.

This blocks the PyPI release (#195) as the same situation will happen when installing a package from PyPI.