Restore on device testing

This addresses the issues introduced in #510 (not being able to run tests on a device).

The first commit links the UIAutomation framework only when needed, e.g. ackowleding system alerts.

The second wraps the `--acknowledgeSystemAlert` method in `#if TARGET_IPHONE_SIMULATOR` to only compile it in when targeting the simulator. This means the included test suite will not build if targeting a device. Thoughts?