Visual diff and link previews

[humitos]

With #465 we deployed a way to re-trigger the setup for the link previews when visual diff is enabled/disabled. It works well, but it seems that the events attached to the elements like mouseover is not listened anymore and the tooltip disappears when you hover it.

[ericholscher]

I looked into this a bit and it seems we're creating multiple events on the node, which I think is causing weird issues. I have a partial fix which I just pushed up, but it still has issues with the previews in the diff'd content.