Merge pull request #207 from wazo-platform/rename_plugins_with_underscore

Rename plugin folders to be valid Python identifiers. Output archives maintain the original names.

reason: Python identifiers must not start with a number and may not
contain dashes and periods. Using valid identifier names allow them to
be treated as modules and allows the use of pytest, mypy and other tools
that do discovery by module. It's the first step to proper testing

Reviewed-by: Alexandre Fournier