Standardize the `jsonHandler` and reduce the use to one `JSON` library

[alallema]

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Pull Request

What does this PR do?

This PR tends to normalize the JSON Library used in this SDK try to gather all the code using a JSON library into a single handler that can be customizable.

PR checklist

• [ ] fixed #253 (TO FINISH)
• [x] Add the possibility to define a JSON through the Config() object
• [x] Remove all usage of a Library without passing by the jsonHandler Class
• [ ] Add a series of tests for the other jsonHandler than GSON
• [ ] Add usage explanation on the README

Notes

• Finish removing org.json.JSON
• Issue with getDistinctAttributeSettings() method who is still messy