Provide example for interacting with NavigationView

[coreform]

[slinzner]

This is going into the next Espresso release, in the meantime use this Action which i wrote for the testing codelab: https://github.com/googlecodelabs/android-testing/blob/master/app/src/androidTest/java/com/example/android/testing/notes/custom/action/NavigationViewActions.java