To simplify j2cl migration and overall speed of development, serverless-workflow-diagram-editor modules json processing should be re-implemented.

It can be achieved in the following steps:

1) copy my apt-based marshallers from a private repo to the`monorepo`
2) adopt models (annotate them, check getters/setters, add custom ser/deser) 
3) replace existing marshallers with generated ones
4) fix/update tests