Integrated DataTables function for participants table (for client side sorting/filtering/pagination). Removed old server side sorting/filtering code.

Fixed csv import (added success url).

Added large csv file for testing import of >1000 participants.

Removed lage csv example file for paticipants (will be sustitute by a test script in future).
Merge pull request #561 from emanuelschuetze/datatables-participants

Datatables for participants table (reworked)
Merge branch 'master' of github.com:OpenSlides/OpenSlides
removed some unused functions
Fixed version history.