introduce iOS testing

This adds automated testing + Travis to the Cocoa bindings & static library. 

 * Moves the iOS test app from [`gl-native`](https://github.com/mapbox/mapbox-gl-native) to this project. 
 * Makes use of [KIF](https://github.com/kif-framework/KIF) for gesture-capable integration testing. 
 * Creates a new basic app in `/test` strictly for tests (and avoids needing GYP for it). 
 * By way of KIF requirements, adds [iOS accessibility](https://www.apple.com/accessibility/ios/) support to accessory views. 
 * Adds [Travis CI](https://travis-ci.org) automation. 
 * Adds some initial compass & panning gesture tests.