Feature notifcations dialog

This PR provides two things:

1) Handling "notifications" related dialogs which appear particularly on iOS 8 devices

2) Support for handling system/privacy dialogs that appear immediately on launch of the app. This is done by using the user-facing launch option: `dismiss_immediate_dialogs: true`, e.g., `start_test_server_in_background(app:'com.company.app', dismiss_immediate_dialogs: true)`

NOTE: For now we don't explicitly document `dismiss_immediate_dialogs` but we can use it on a case-by-case basis with individual customers. The reason for this is that I think we can get a better / easier to use solution going..