Use flake8 instead of pep8. Orderd the imports with isort

* changed the fab-command pep8 to check
* checked and fixed any code with flake8. Also the urls.py
* checkt the projector app with pylint
Merge pull request #894 from ostcar/pylint

Cleanups
Add prototype of full text search integration in openslides
Allow for empty title and text body, fix pep8 errors
Full text search with haystack and whoosh.

Updated THANKS file.
Portable: Added haystack and whoosh.
Fixed Norman comments.