Read python files directly from CLI and GUI

[erwanp]

Following #28 , Python files can be converted in a suitable Yaml file, with STONE format, by sim2stone.

This PR implements it automatically when :

1. Loading Python files from the command-line-interface (CLI) with

boulder some_file.py

2. Loading Python files from the "Drop or Select Config File" in the graphical-user-interface (GUI)

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Therefore:

• .py can now be read directly by Boulder.
• A corresponding YAML file is generated on-the-fly.
• If another YAML file already existed, it is compared and a warning message is raised. If different, the on-the-fly YAML corresponding to the .py file is generated next to the existing YAML file ; the existing YAML file is not replaced.