Fix per default selected Groups in polls

[Elblinator]

Current behaviour:
If a poll is started and something else than the default group/s is selected for this poll, then these groups are remembered the next time you start a poll, in contrast to the actual default group/s.

Reproduction:

1. in a meeting:
2. navigate to settings > Elections
3. select Admins for "Default groups with voting rights"
4. Navigate to Election-list > one election
5. open the dialog of "new ballot" and select delegates and staff as "Entitled to vote"
6. create the ballot
7. start creating a new Ballot
8. Now the groups delegates and staff are preselected in "Entitled to vote"

(The votes in motion and Topics have the same behaviour)

Wanted behaviour:
If a new Ballot/Vote is being created the groups which are selected as the default group in the settings should be preselected in "Entitled to vote"