This commit introduces a few changes regarding users accessing
communities:
While the APIs still exist, community invites should no longer be
used, instead communities should merely be "shared".
Sharing a community to users allows users to "join" the community,
which in reality makes them request access to that community.
This means, users have to request access to any community, even if
the community has permissions set to NO_MEMBERSHIP
Only difference between ON_REQUEST and NO_MEMBERSHIP is that
ON_REQUEST communities require manual approval of the owner/admin
to access a community. NO_MEMBERSHIP communities accept
automatically (as soon as owner/admin receives the request).
This also implies that users are no longer optimistically added to the
member list of communities, but only after they have been accepted.
This introduces a bit of a message ping-pong for users to know that
someone is now part of a community
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