Add paging to rounds index

[Closes #63]
Probably just the length, right? The total number of pages isn't gonna change unless the number of rounds changes, even if the actual rounds are different.

> On Dec 29, 2014, at 12:05 PM, Geoff Schorkopf <notifications@github.com> wrote:
> 
> In app/assets/javascripts/controllers/rounds_index_controller.js:
> 
> > @@ -34,12 +44,33 @@ App.RoundsIndexController = Ember.ArrayController.extend({
> >      }
> >    }.property('sortAscending'),
> >  
> > +  isFirstPage: function() {
> > +    return this.get('page') == 1;
> > +  }.property('page'),
> > +
> > +  totalPages: function() {
> > +    return Math.ceil(this.get('arrangedContent').length / this.get('perPage'));
> > +  }.property('page', 'perPage', 'arrangedContent.length'),
> Interesting. Do we want to keep track of the property 'arrangedContent.length', or just 'arrangedContent'? Does it matter?
> 
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