Testing TODOs

[osa1]

In this issue I'm listing issues that I'd like to test as a part of the automated tests (cargo test):

• msg to user from second client appears in tiny as writing to yourself #271 (cae4666)
• Prefix without '!' assumed to be a server #247 parsing is already tested, but we should also make sure messages without ! in the prefix are shown in the correct tab.
  (c53d98e)
• Update dependencies #275 currently doesn't run at all, yet it passes CI. We should probably run an IRC server locally and try to connect it.
• Channels/nicks need to be case-folded on match #248