Hanling of Q object in filtering

 The _filter_or_exclude() function can receive filtering expressions from
its args or kwargs arguments. The first one is used for passing in Q
objects and the second one for expressions. Up until now we were not
dealing with the Q objets and only thought about the expressions.  Now
this code takes care of the Q objects as well.
Removing commented out code
Adding handling of ForeignKey in _filter_or_exclude()
Merge branch 'master' into support_for_Q_and_foreign_key
Enhanced some comments to make more sense; added explicit test for newly added code part and shortened test duration by some 10ths of seconds; PEP8
Merge pull request #1 from swisscom/support_for_Q_and_foreign_key

Support for q and foreign key