frontend: nicer submitter identification
    
    .. both in web-UI and in backend's redis database.
    
    For normal builds (submitted via web-UI or API) we still print the
    copr user link (pointing to list of user's copr projects).
    
    But for webhooks - where we don't know build.user_id - this isn't
    possible.  So if the webhook method allows this (.. so it sets the
    'build.submitted_by' field) print that nicely in the web-UI
    instead.