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