Full support of the readstate object

Complete changelog:
- added a new API URL : GET /user/articles/:guid, to get the content of
a specific article without downloading the content of the other
articles in the feed
- updated readstate document format to contain more information, thus
reducing the number of requests needed
- added couch-wrapper function to update a the read property of a
readstate object
- removed an old non necessary CouchDB view
- updated frontend to take into account API changes