Bug 1015390 - [SMS] Implement new startup loading events

- Replace the original performanceTestHelper events with new startup loading events  
no, I think it's fine, because from what I read on the MDN page https://developer.mozilla.org/en-US/Apps/Build/Performance/Firefox_OS_app_responsiveness_guidelines it looks like moz-content-interactive needs to happen after moz-app-visually-complete (because it depends on it)