Last updated field in superhero model

I added an automatically updated field to the superhero model, lastUpdated - whenever a field is modified, this timestamp will automatically update.

I also added a new jQuery module - jquery.timeago.js - and added a time field to the profile panel

![screen shot 2014-04-12 at 8 10 36 pm](https://cloud.githubusercontent.com/assets/58883/2688450/e70da554-c2a0-11e3-8394-e23cb63797d9.png)