The list would keep the previous results in memory, forever, and the list
would grow each time a new request was made (even with results from
unrelated servers)…

This allows the user to join channels containing forbidden characters
in the local part, like #r&d or #group/project.

fix #3067

ref #3067

fix #3177

For example if we are talking in private with nick Joe from
room #foo, and then we leave that room, we start receiving Joe’s
message from the server-wide JID

e2e tests included!!!

ref #2556