Rework (projector) template with bootstrap.

- Always use templatetag 'absolute_url' instead of (depricated) 'model_url'.
  Search and replace all old arguments: edit -> update, view -> detail, delete
- Fixed bug in setting default value in 'absolute_url' templatetag
  (default value is defined in models.py only).

Updated 'backend' template.
Merge pull request #901 from emanuelschuetze/newprojectortemplate

Rework projector template with bootstrap
More projector fixtures

* Update projector when polls are updated.
* Update projector when assignment candidates are updated
* Update projector when motion submitter are updated
* Fixed the assignment publish poll view
* Added projector.api.register_slide_model
Merge pull request #899 from ostcar/projector

Added projector.api.register_slide_model
Some template fixes and improvements:

- Fixed absoluteurl in motion detail template. Renamed '_edit' to '_update'.
- Fixed wrong projector link ind assigment poll template.
- Improved assignment projector slide.
- Fixed #884: Add PDF note to translation string "Show paragraph numbering"
Merge pull request #905 from emanuelschuetze/projector-fixes

Fixes and improvements for projector and template
Cleaned up utils
Merge pull request #895 from ostcar/utils

Cleaned up utils
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
added possibility to show pdfs on the projector