Default everyone group

[d-513]

Some services want a group to be present for config, so a default group that everyone gets assigned to would be useful.

[nitnelave]

For this feature, the most elegant solution I see going forward is:

• on startup, if the "lldap_everyone" group doesn't exist, create it and add every existing user to it.

• when creating a user, add it to the group.

• prevent deleting the "lldap_everyone" group (like lldap_admin and lldap_readonly (need to add that one))

• in the web UI, when creating a user, have a default checked checkbox "add to lldap_everyone group", and propagate that in the query.

[binaryben]

What about allowing a config option to define a number of groups (0 or greater) that every user is added to by default?