Use the `exception` log method for better exception logging. This change the log
level to 'ERROR'

All import processes now use a general try-catch during the import of each data
item. This ensures that even in the event of an error (due to a malformed data
piece for example), the import process will continue.

Errors caught this way are logged at the debug level.

- add tox for easier reproduction of travis builds
- add idempotence to install_client_deps.sh if CI=1
- mov modules into src/
- update setup.py to install everything as separate modules
- add docs and qa tox jobs
- update documentation

Todo:

- merge django-representatives
- merge django-representatives-votes