Question: How to extend DefaultLeapFrames with new operations

Hi,

i am currently working on an extension of the `DefaultLeapFrame` class. I want to give it 3 operations which I think would help several people to get things rolling: explode, implode and join. I do this to be able to join additional information to data which is sent to the serving rest-server for predictions which can then be used to create new features that are needed for my pipeline.

I have a first draft for which i touched the following files:

1) `LeapFrame.scala` (adding abstract methods there)
2) `DefaultLeapFrame.scala` - _extends LeapFrame_ (implementing them there)

When I try to compile, it gives me one error, complaining that I did not implement the new methods in the `RowTransformer` (also _extends LeapFrame_ ).

So my questions is: do I need to add those methods to the `LeapFrame` which is higher in the class hierarchy or is it enough to add them only to the leaf `DefaultLeapFrame` (which i found to be used in the serving project)? The `RowTransformer` is as far as i currently understand it only important to provide dataframe functionality for the Transformer parts of the Pipelines we want to model. So to my understanding, I would not need to add those methods there. Is this correct?