add methods for removing data cruft

Issues:
* According to our code, topics.json should not include nodes of kind in ["Separator", "CustomStack", "Scratchpad"]... but it does.
* node_cache.json is quite large, but it is easily computable from topics.json (fast) and only gets computed on the first non-cached request.
* IDOC deployment requires a package size of less than 10MB

In this branch, I:
* Created a function to remove the topics.json cruft, then called it once (manually), then saved the (updated) json file.
* Delete node_cache.json, and compute it (on the fly) from topics.json, when needed.