Logging on JNI level

In order to be able to debug on the JNI level, we can log to the ordinary Android log. In this PR, I have added logging of all calls to shared group method. This is work-in-progress - we should be able to log all calls in the other modules and log values of essential variables and parameters.

@bmunkholm @cmelchior @emanuelez 
shouldn't this comment say `// JAVA` instead?