Added Logging

Just as promised: I added logging to the application - both console as well as file logging. I also added another argument "--loglevel" which can be filled with "DEBUG, INFO, WARNING, ERROR, CRITICAL" and the loglevel will be set to the specified value.

(I also made a little change to the search.py which uses only the "newznab_host"-setting for the URL (without adding "http://" in front) when the user already specified "http://" in the settings)