Instead listen for if the accessibility service is running or not by
implementing AccessibilityStateChangeListener.
This seems to work smoothly when turning on or off TalkBack.

This should also improve startup time.

Change-Id: I3eb7d6cb9c9c1618afbb59675e4e089c9159019c
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>