Currently, the mentions only track the chanID and MsgID.
However, when we part a channel the chanID becomes orphaned.
Considering that mentions from a parted channel probably aren't
that relevant, let's automatically clear them when we part.
Should the user really want to look at them again, they can re-join
the channel and get the scroll back that way.
Several ES6 additions are only available in strict mode. Example:
> SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode
Strict mode was also enabled in a few of our files already, and it is a good thing to have anyway.
Currently, for join/part/kick/nick/... the server will send an updated list of users and the client will re-render the list entirely. This ends up being a very expensive operation when joined on large channels and causes the client to slow down a lot.