Added process manager to handle running multiple processes and multiplexing stdout/stderr from each process.  Code borrowed from Honcho.
Modified extension installer to keep a list of installed extensions.
Removed ExtensionScriptBuilder.  Instead extensions are processed based on the list of them stored in the context.  Modified the StartScriptBuilder's write method to process each extension calling the 'preprocess_commands' method.  This returns commands that the extension should run once as a part of the startup process.
Added a global extension processor method.  Added SaveBuilder and tests.  Altered plugin structure a bit, it's still in flux.
Refactored to use global _process_extension method.
Refactored to use global _process_extension method.
Flake8 compliance.
Refactored load_extension, process_extensions and rewrite_cfgs into utils.  Added tests.
Added load_env and load_processes, plus tests.