feenkcom PythonBridge extensions

[akgrant43]

As discussed:

• Signal python exceptions in the calling process, not the server process (which effectively locked the image)
• Don't hang if stdout / stderr subprocess output exceeds buffer size.
• Allow the runtime files to be easily copied to a separate location (doesn't require git repository to be present, and doesn't modify the git repository; removes the circular symbolic link)
• Allow the pipenv path and working directory to be specified in the settings. (Especially useful on Mac where there doesn't appear to be a standard python installation).
• Add support for the DAP debugger
• Add support for custom proxy classes.
• Automatically stop the python server on pharo shutdown.
• Report error information from the subprocess when something goes wrong (not demoed).
• Fix a few of the automated tests.