WIP: Implement link preview
This is a similar MR than !121 (closed), however I did not have to push there some changes, so I created this considering the previous commit, and edited them.
The original description of the MR:
This merge request merges cleanly with the master branch. It introduces the link preview patch by Mads Olesen with some changes by myself. The patch was originally discussed in #662 (closed).
With this patch evince shows a preview of the link destination in a popup.