have group members saved by auth token id in backend, not name

[Dedicated-RAM]

If I join a group and then change my username, the previous username is in the group and I can join the same group with my new username.

[Dedicated-RAM]

to fix:
On form submission:

• get user.uid of person who submitted the form instead of displayname

On view groups page:

• Convert user.uid to display name using