add restrict camera example

[tobrun]

This PR adds a Viewport limitation example from mapbox/mapbox-gl-native#3602. Since this feature is only found in the upcoming release, I bumped the SDK dependency to a SNAPSHOT.

[cammace]

lookin good to me :)

[langsmith]

There are two tweaks I made. No problem if they shouldn't be included for whatever reason.

1. I like the geographic diversity of the app. We already use Iceland in the "Animate marker position" example, so I chose Australia for this example.

2. I added the camera target crosshair to show where/how the restriction is happening. I liked it in the test app and thought it'd be good to have in the demo app.