#2 Sort routes

[Dominik Kallusky]

Every route has a set of attributes like total time, walking time, number of transfers.
It should be possible to sort all routes according to one or more(!) of these attributes, by clicking on one of the buttons on the top, for example.
This only pertains to the ViewAlternativesView.
Start off with only one attribute and then add the multisort functionality later.