Use BySelector and UiObject2

`UiObject2` provides some more feature like [`getParent`](https://developer.android.com/reference/android/support/test/uiautomator/UiObject2.html#getParent()), [`getChildren`](https://developer.android.com/reference/android/support/test/uiautomator/UiObject2.html#getChildren()),... that current `UiObject` doesn't have