Display timestamp in "Last edited" column

On the dashboard, under the "Last edited" column we currently show: weeks, days, since the last edit.

Instead, let's show the timestamp of the last edit in the format (written month, day, year) e.g. October 4, 2009

![screen shot 2013-08-20 at 2 54 03 pm](https://f.cloud.github.com/assets/1521387/993346/2bb03b08-0998-11e3-9328-23d781330c67.png)