Notifications

/cc @adgad @railsagainstignorance 

An API to add notifications to an individual users' queue. For the moment I've just allowed notifications against favourites.

So, for every favourite you can collect notifications,

    curl -iX GET -H 'X-FT-UID: mattc' localhost:3000/user/notifications/google

.... which will be empty until we hook up something to push to it.

For now we can manually push a notification to that queue then do another GET and you should see an item in the queue.

    curl -iX PUT -H 'X-FT-UID: mattc' -H 'Content-Type: application/json' -d '{"uuidv3":"google","item":"ce06f15a-4f90-11e4-908e-00144feab7de"}' localhost:3000/user/notifications

Clear the list (say, once the user has visited the favourite) - 

    curl -iX DELETE -H 'X-FT-UID: mattc' localhost:3000/user/notifications/google