ui: improve Notification component

[mdonadoni]

[...] it would be even better to have a component similar to Notifications which would simply display these kind of messages and select an appropriate icon depending if it's a warning, info or an error. In profile page we use it exactly for this purpose, but it's not ideal since it have an additional logic to display the messages from getNotification selector. I think it would be nice to decouple it and use a dumb notification component everywhere in these kind of cases [...]

Originally posted by @audrium in #281 (comment)