context 2.0 - JSON schema

[louisdegaste]

This PR is a follow-up to PR #1566. It contains only the features of context V2 related to JSON Schema implementation.
Because the context V2 enables significantly more complexity in the cookiecutter.json schema, it becomes necessary to have a more robust and unified way of defining the structure of the cookiecutter.json file. This is why we want to use the python package for JSON schema to do so. This PR includes :

• Definition of the V1.0 Schema (pass all schema)
• Base definition of the V2.0 Schema:
• Tools for inferring schema version and validating the structure of a cookiecutter.json file

[klamann]

Hi @simobasso, we are still eager to make some progress with the new cookiecutter.json format that we proposed in #1567, and merging this PR would be the first step to make this possible. We've split the original PR into the smallest possible parts that so that it's easier to review. Would you like to start with this one?

[malarinv]

@simobasso bump