Nicer and more efficient notifications

Pushes notifications out of the topbar and uses `angularJS-Toaster` to display them as unobtrusive overlays.

Some refactor of `notifier` came with that, mostly things are easier now (with the removal of the directive `currentMessage` and the like).

The css of the toaster has been taken over and customized - some pieces have been rewritten in scss as well.

The main benefit of that approach is that we are able to display more than one notification at a time and they are also a bit more prominent that way. (and of course prettier!)

The API of `notifier` didn't really change, apart from that it takes also an optional title now

``` javascript
notifier.success('Message body', 'title')

// title is optional, available functions are success, info, warning, wait and error
```