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.
Fixes the /part command closing the wrong window. The current implementation simply passes all arguments to slate, which ended up parting every arguments.
This changes the command to `/part message`, and always parts the current window. This will be fixed further once irc-framework is merged.