Display notifications in the console

[vincent-zurczak]

Once #81 is done, we should reuse the web socket client to display notifications.
This may require we rework our in-memory model. Indeed, everytime we change the page, we reload from the server all the information. Except that notifications are not (and will probably not) be stored on the server side. They will be propagated to clients on the fly.

So, rather than loading from rest services everytime, maybe we should store our model in memory and update it when necessary. What we may keep in memory is the list of applications and the associated notifications. Other parts may be loaded on the fly.