Allow FirebaseListAdapter class to iterate object keys

[ShamariFeaster]

I have a scenario where I want to be able to quickly check for key existence and because of that it was desirable to use object keys as the value (like a hash table).Essentially this means I needed to be able to extend FirebaseListAdapter using a mModelClass class of type String.

To support this functionality, I modified FirebaseListAdapter with a function parseNode

private T parseNode(DataSnapshot dataSnapshot){
                String key = dataSnapshot.getKey();
                T newModel = null;
                if(!(FirebaseListAdapter.this.mModelClass == String.class)){
                    newModel = dataSnapshot.getValue(FirebaseListAdapter.this.mModelClass);
                }else{
                    newModel = (T) key;
                }
                return newModel;
            }

Now in all of the ChildEventListener callbacks the model variable gets assigned the output of parseNode and the adapter is able to handle iterating over object keys. I just figured it's a pretty minor change to the class and it helped with my case so maybe it would be useful for other people.

[ShamariFeaster]

thanks!