Change support button in a motion

[Elblinator]

Current behaviour:
If a motion (e.g. motion B) is in a state which can be supported and

• the participant is allowed to support motions
  • support/unsupport button is visible
  • the number of supporters is displayed
  • the list of supporters can be opened
• the participant is NOT allowed to support:
  • the support/unsupport button is not visible
  • if the participant pressed support before, the support still counts and cannot be revoked (bc the unsopport button also is not visible)
  • nothing about the supporters (amount and number) is displayed

Wanted behaviour:

1. Like the submitter of a motion, the supported of a motion should always be visible for a participant who is allowed to see this motion
2. A participant should always be able to withdraw their support
3. If a participant who is not allowed to support anymore supports a motion, the participant should not count in the "supporter list" and should not be displayed in the list

@emanuelschuetze could you comment on what is your desired behaviour for openslides?
Dependent on the plan we need a new row in the group-matrix for 1., and 2. could be solved if OpenSlides just 'forgets' the support in 3.