Fixed unicode decode bug in task overview.

Fixes https://github.com/4teamwork/opengever.phvs/issues/27

Bug happens only in single client setups. He appears if a task is displayed who has a special character in its title or its breadcrumb.

@lukasgraf 
This comment is wrong - you never encode *to* unicode, you encode unicode to a bytestring, or you decode a bytestring to unicode.