User reading history

This is a simple JS module that tracks user reading history and persists to localStorage.


### Notes
- It currently stores the last 100 read articles, keyed by their shortUrl in local storage. 
- Next steps will be to persist this data through to Identity against their Guardian profile. 
- We also would like to track the top n sections a user visits.
- Security implications?

/cc @indeox according to Matt this may be of use to the work your doing as well?

!['Packing'](http://sprinklesinsprings.com/wp-content/uploads/2011/08/packing-gif-small1.gif)