Chen reorder stops

https://trello.com/c/1lUM4ww1/46-as-i-user-i-can-reorder-stops

![update all stops order after reorder a stop](https://cloud.githubusercontent.com/assets/3759510/5130262/3b83d058-70b7-11e4-9f6e-c0ed60564b21.gif)

no need for instance variables since you always redirect. I would recommend:

``` ruby
tip.reorder_stops_after(stop, proposed_order)

private

def proposed_order
  params[:stop][:order].to_i
end
```