graphmod/webcommands: use generic DAG walks Changes graph() to colorededges(), which operates on the new generic DAG walks and adds color and edge information needed by the web graph. This is in preparation of adding DAG walk filters, like the linear run collapser in the next patch. The idea is to have a bunch of changelog walkers that return basic data. Then we can filter this data. Finally we add edge and formatting info suitable for the output media we want to target (glog, hgweb).