New and improved repo punch card

[mpdehaan]

It might be interesting to have a graph that shows a punch card like GitHub's but showing everyone who is working on the repo - "darkness" could key off the number of authors per day.

This might be something we want to show on the repo "homepage" (along with total stats and stats for the time period) rather than the graph page.

In user view, we should also show the user's individual punch card.