Dialog for creating departure notifications

One feature we've talked about adding, and that I think I would use, is the ability to create a notification at a certain interval before a given departure.

This adds a dialog that's opened when clicking any item in the departures list:

![device-2014-02-26-195405](https://f.cloud.github.com/assets/227091/2275477/6a2dff2a-9f28-11e3-9de7-8c74dfb2d1d9.png)

Actual functionality (keeping track of all requested notifications, possibly checking for updates to the departure time, triggering the notification at the right time) would take more discussion and work.