Updated docs

I added a warning about returning non-utf8-encoded strings from within ``def __unicode__()``, as I found it resulting in a 500 response and a plugin instance marked as <Empty>. After returning as UTF8 everything worked as expected. If you can't confirm these issues to be related or feel that the addition doesn't make sense for documentation readers, feel free to drop it.
Alias plugin fix for CMS without multilingual support
Merge pull request #3363 from sthzg/patch-2

Updated docs
Merge pull request #3371 from donce/language_fix

Alias plugin fix for CMS without multilingual support