Get last location now prefers updates within last 60 seconds.

* Returns most accurate update in the last 60 seconds.
* If no updates in the last 60 seconds, returns most recent.

Adapted from http://android-developers.blogspot.com/2011/06/deep-dive-into-location.html
Merge pull request #8 from mapzen/chuck/get-last-location-should-prefer-recent

Get last location now prefers updates within last 60 seconds.