Add a MultiMergingTransformerFilter

Based on the MultiMergingTransformer implementation, but allows for algorithms to return a boolean which sets the 'filter passed' property for affecting the control flow.

A new test checks an example instantiation MultiMergingTransformer, as well as one for MultiMergingTransformer, which existed as an algorithm before but was not tested. To make this test more obvious the IntDataProducer example algorithm now has a configurable value property.

/cc @nnolte