Draw a line on the map as the user walks

This is a first-iteration at requesting location updates from FusedLocationProviderApi. It draws on the map, and makes some updates to the surrounding codebase.

-   Google Play Services 5.0.+ is now required.
-   We now use Java 7 instead of the default, 6. Java 8 isn't supported
    on Android.
-   The main activity is now reponsible for connecting to Google Play
    Services.
-   We now extend MapFragment, allowing us to properly determine when
    getMap() has likely been constructed, and allowing us to encapuslate
    the display of routes.

A number of issues currently exist.

-   Error handling is very poor.
-   Tracking stops if the activity is destroyed, eg, when the screen is
    turned off for an extended period of time.
-   Low-accuracy readings may block high-accuracy readings from being
    recorded if they're within 10 meters of the high-accuracy reading.
I'd avoid null, but it appears to be convention in the Android libraries. Eg:

- When `onCreate()` is being called for the first time, the state `Bundle` is `null`
- `getMap()` is `null` until `onCreateView()` is called, or when Google Play Services is unavailable

I could have this be `Optional<Polyline>`, but it wouldn't match the surrounding code that I have to use null checking on.