Do not create PeerSession for groups we created
Instead, if a contact we are adding is already in one of our groups, re-create the appropriate session. Also, when removing a creator of one of our groups, auto-dissolve the affected groups.
Test instructions (has automatic integration test as well):
- Add a contact (B), create a private group and share it with the contact (B).
- Then both contacts (A and B) remove and re-add each other.
- When the creator (A) tries to share the group, check that no crash happens, other contacts can still be invited and join the group
- Check that the group is dissolved for (B) who can not be invited again
Closes #1483