Added suport for animation’s listener with an example

Hi! 

I use this library frequently and I think it’s really useful. But something I’ve missed so far it’s a group of callbacks to listening for when a row is expanding or collapsing (starting or ending). For that reason, I’ve added a simple interface to handle it:

public interface SlideExpandableListener {
    public void onStartExpandAnimation(View view, int position);
    public void onEndExpandAnimation(View view, int position);
    public void onStartCollapseAnimation(View view, int position);
    public void onEndCollapseAnimation(View view, int position);
}

This interface could be implemented and linked to an instance of SlideExpandableListAdapter as follow:

 slideAdapter.setExpandableSlideListener(new SlideExpandableListener() {

            @Override
            public void onStartExpandAnimation(View view, int position) {
                Log.d("slide", "start animation expand with item position: " + position);
            }

            @Override
            public void onEndExpandAnimation(View view, int position) {
                Log.d("slide", "end animation expand with item position:" + position);
            }

            @Override
            public void onStartCollapseAnimation(View view, int position) {
                Log.d("slide", "start animation collapse with item position: " + position);
            }

            @Override
            public void onEndCollapseAnimation(View view, int position) {
                Log.d("slide", "end animation collapse with item position: " + position);
            }
});


Also, I’ve faced a few problems trying to compile the project with the current version of Android Studio (0.8.14). So I've had to make some changes to get it to work.  

Greetings,
Victor.