Add a button to download a sample Journey via API call and turn it into a bunch of Stages

[iswheeler]

Calling the initWithLeg(Leg leg) function on each Stage with the Leg created from the /plan-journey API call--to help the frontend team test their Stages and make sure they work with the API!

[iswheeler]

Almost ready for initial testing--we'll integrate this very soon by adding the initWithLeg call once that's ready inside the walking and on-bus stages.

In the future I'll need to integrate this with the existing "Search for a destination, choose a route, and get directions" UI path instead of just hard-coding LatLng coordinates in the /plan-journey call.