Add socket traffic stats to listsockets

I was able to get this to work by recompiling the module, placing it in `datadir/modules/` and putting the edited index.tmpl in `datadir/modules/listsockets/tmpl/`

My only peeve right now is that sometimes the data columns line-break between the number and the unit, but I don't feel like messing with that right now, and it works well enough I think.

Thanks to @psychon for the initial code to add the data usage to the listing sent over IRC. The following stumbling around in the dark to find the right tmpl to edit was all me, though, but now I better understand how ZNC works (a very little bit).