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.
Fix wrong url_name_args in ItemDelete view. Fix #910.
Merge pull request #896 from emanuelschuetze/search

Search
Merge pull request #912 from normanjaeckel/Fix910

Fix wrong question_url_name in ItemDelete view. Fix #910.
Cache the results of ItemDelete.get_answer_options

Fix #911
Merge pull request #913 from ostcar/issue-911

Cache the results of ItemDelete.get_answer_options
Add CKeditor to the agenda item text field
Merge pull request #914 from rolandgeider/issue-626

Add CKeditor to the agenda item text field
Insert new feature: attachments for motions.

Fixed #522. Database struture changed.
Merge pull request #908 from normanjaeckel/MotionAttachment

Insert new feature: attachments for motions.
New feature: couple countdown with list of speakers

'Begin speach' button starts countdown, 'end speach' button stops countdown.
Clean up main.py and move code to __main__.py and utils/main.py.
fix gui/portable for pull request #903
Some changes in __main__.py and utils.main and other.

Reinsert --no-browser option.

Move some code to utils.main.

Some other small style changes.

Fix merge conflict misstakes.

Change settings behavior. Add tests.

Fix rebase problems.
Changed begin speach behavior. Fix merge conflicts. Add tests.
Merge pull request #903 from normanjaeckel/CleanUpMain

Clean up main and move the code to __main__.py
Merge pull request #920 from normanjaeckel/CountdownAndAgenda

Countdown and agenda