Show the estimate time to the waypoint

I've added a new method `getTimeToDistance()` to get the estimate time to the waypoint.

![sc1](https://cloud.githubusercontent.com/assets/7722222/5564280/2afd2c40-8eb5-11e4-8886-c51affb21f6a.png)
![sc2](https://cloud.githubusercontent.com/assets/7722222/5564281/2dc5782e-8eb5-11e4-9951-87a390a33591.png)