Statistics for each patch in a patchset

[JelteF]

This suggestion came in from the mailinglist:

a per-patch breakdown of the number of addition and deletions for the
last patchset version posted, one line per patch.  This would appear
in a tooltip on the column for the totals, to avoid interface
clutter.

I think the exact way to display this could use some thinking/protyping to come up with something that works well. Maybe it should not be visible on the commitfest page, but only on the patch details page. But showing stats for each of the patches in a patchset somewhere seems like a good thing.

Each patch could be a link to the patch on github, which could reduce the amount of clicking necessary to view the one that you're interested in.

This would need cfbot changes too, because that's where we can gather these stats.