Added changes to notify websocket listeners of alert dialogs.

One thing to keep in mind: iOS and Android treat dialogs differently. iOS "system" dialogs can be triggered from the application under test as well as from external sources (the system). However, Android treats dialogs as any other window. So, to make this work, the bootstrap app looks for windows with the package name of "com.android.systemui". These are dialogs that the system has instantiated, but not the app.

So, for example, if we had the same application written on both platforms, and they both had a login screen, and you click on the login button without putting in a username. On iOS, you would be notified if they used a standard system dialog, and you would not be notified on Android. However, if the system put up a low battery dialog, it would be detected on both systems.

So... The main reason for implementing this is to stop failing tests from unintentional dialogs appearing during an overnight test.

Updated call signiture to instruments.
Merge pull request #624 from mutualmobile/websocket_notifications_for_alerts

Added changes to notify websocket listeners of alert dialogs.