Replies should truncate replied-to message

[eclairevoyant]

Replies display the entire contents of the original message instead of e.g. a couple of rows + ellipsis or whatnot. This leads to a lot of vertical space taken up by the reply, especially if the original message had an image.

Now that #452 (adds :replied command) is merged, I think it makes sense to truncate the replied-to message above the reply.

[Elec3137]

I think this would be best as a configuration option, since having the whole message is also very useful if you have the screen space.