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.

Also:

- code was PEP8'ed
- tests were added,
- untested code was removed,
- setup.py was fixed and requirements.txt is gone,