Reduce number of `IdentityDictionaries` in `AlgaNode` by having sub-classes

[vitreo12]

Basically, develop subclasses that pair common functionalities, and use those in IdentityDictionaries:

AlgaInOutNodes {
    var <inNodes;
    var <outNodes;
}

AlgaNode {
    var inOutNodes = IdentityDictionary(param -> AlgainOutNodes);
}