Prevent superadmin to see non participants in motion > multi select > set submitters

[Elblinator]

Description:
as superadmin: in motions/amendments > multi-select > set submitters
if the list of submitters is opened all accounts are displayed and every account can be seleced, even accounts which are not participants of the current meeting.

Current behaviour:
as superadmin: in motions/amendments > multi-select > set submitters
every account can be added (and afterwards be removed) as a submitter, without adding them to the meeting as participants.

Wanted behaviour:
The list for the potential submitters should be the participant's list and not the accounts's list.
the superadmin should not see accounts who are not in the meeting