Adresses issue #30 and #45

- result_unpublished -> result_published
- disable_abstention -> enable_abstention

* Added auto election result publication per default
* Can be changed to manually in advanced tab
* published results can no longer be unpublished
* database field for publication state is now bool

* added threading for invitation emails to avoid wsgi timeouts for big elections
* added email success/failure feedback for the sending of invitations in the session's management. This is done asynchronous with django channels and modals and alerts that show the failed email addresses

removed stusta domain references in the code and moved it to the config file, moved default email address (used when no manger email is set) to the settings file

issue #22: prints qr code of the meeting link onto the pdf when available, removed json export since its redundant and one small model label update

Send E-Mail When Voting Period Starts and use templates for all emails that are sent to users, Issue #10, Milestone !1

* option to enable voters to apply for elections, added new option in the election creation page
* CSV files can now be used to scale up voter creation for the Hausadminwahl

Issue #2: Added possibility to add anonymous voters for voters where the email is not known. The tokens can then be downloaded via PDF, printed and distributed analogue.

we actually don’t know who is a winner