Fix an issue with notifications being shown when fetching old lines

@xt, does this fix the issue for you?

While we're at it, fix the annoying jump-to-bottom when loading more lines.
Add nick to highlight notification from channels
Merge pull request #181 from tribut/notification-nick

Add nick to highlight notification from channels
Merge pull request #171 from lorenzhs/fixduplicatenotifications

[WIP?] Fix an issue with notifications being shown when fetching old lines