Spinner service and directive

Implements a little spinner service, which right now is solely called by a Resource. That means that everytime an external request is made, we spin the spinner without having to care about doing this manually. Very handy. (the $promise API to do this is pretty nifty I must say!)

We display the spinner in the navbar for now - which also determines its color. It's therefore not really reusable at the moment, but that will come if we ever need it.

Fixing a bug in the collapible behavior of the navbar buttons. The calculations where slightly off - the inclusion of the spinner made this worse and more apparent.