Add support for speed limit annotations

[coxchapman]

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Expected Behavior

Once @karenzshea adds the speed limit annotation to the Mapbox Directions API, we should expose it to the Android library.

Detailed Description

I see two things to accomplish this:

• Add maxspeed to the list of supported annotations here: https://github.com/mapbox/mapbox-navigation-android/blob/master/libandroid-navigation/src/main/java/com/mapbox/services/android/navigation/v5/navigation/NavigationRoute.java#L282-L304
• Get input from @karenzshea as to whether there will be a new JSON block to integrate or whether it will be returned in an existing array

cc/ @danesfeder @osana

[danesfeder]

Add maxspeed to the list of supported annotations here: https://github.com/mapbox/mapbox-navigation-android/blob/master/libandroid-navigation/src/main/java/com/mapbox/services/android/navigation/v5/navigation/NavigationRoute.java#L282-L304

Yeah, first this will happen here:
https://github.com/mapbox/mapbox-java/blob/master/services-directions/src/main/java/com/mapbox/api/directions/v5/MapboxDirections.java#L553-L572

Then, we will update the NavigationRoute (wraps MapboxDirections in the Nav SDK) code to reflect the same.

[osana]

addressed by #772 and #777