REFACTOR - Do the de-referencing in the get_schema_template function

[MonikaVo]

Having to de-reference definitions adds quite a substantial amount of extra logic to the already complex process of translating the schema (all the checks for $ref that you do below). I would advice to do the full de-reference separate before calling this function as a separate task, so all references are replaced by the actual sub-schemas and you don't need to worry about that here.

You can even use an existing tool like replace_refs from jsonref library (I am already using it for the limitations, see here).

Originally posted by @ramirezfranciscof in #182 (comment)

Preparations are already done in comments in the server_manager.py. However, this causes a comprehensive refactoring of the code.