Add last-commit "badges" to all github repos

[avelino]

reference thread: #3154 (comment)

[maguro]

This is a pretty cool idea.

The first thing I do when I come here is to open a bunch of tabs, one for each project, to see various metrics. I think it would be useful to have a set of badges per project so I could see at a glance the lay of the land and drill down to the projects that I'm most interested in.

[Bahry67]

Ok