Reminding for update (in chat) at interval

[MorrowShore]

This feature is pretty self-explanatory. Once every 3 hours, a new system chat message will appear to notify the user if their client is out of date. This message will only be visible to the out-of-date user, and should include a link to the Drawpile website or GH releases.

The previous idea was to have a pop-up, but that may be too annoying.

Here's another possibility that would probably annoy more than a muted chat message.