Pre-codegen massaging of JSON schemas

[jacoscaz]

This PR refactors codegen scripts to share as much pre-codegen "massaging" of the official JSON schemas, including:

• addressing misspellings and other errors in the official schema packages released by the OCA, such as the misspelling of Celsius that caused OCPP 1.6 Validation fails for StopTransaction message due to invalid unit "Celsius" #7
• merging identical child schema definitions into a shared dictionary of schema dependencies, which in turn helps with deduplicating code in the generated files and results in a 50% decrease in file size