Beeing able to change display name of a contact

[yennor]

Is your suggestion related to a problem? Please describe.
I couldn't find an issue already describing this, so I open my own.
I've got some contacts which use user names I just won't be able to recognize or distinguish (think about john1, john2, test123). So in the 1:1 room I've tried to rename the room name, which ended in an edit war. There's already a ticket about that: matrix-org/matrix-spec#810 .
But also there seems to be no possibility to change in other rooms, what name is displayed to me for certain users.

Describe the solution you'd like
I'd like a possibility to set a displayname for any user (contact) myself. eg. When john1 writes in the 1:1 room, and in any other room, I always see "John Smith".

[t3chguy]

Duplicate of https://github.com/matrix-org/matrix-doc/issues/690