feat(Poetry): Analyze also the development dependencies

Implement the analysis of development dependencies on a best effort
approach. In the long run it seems to be reasonable to directly support
the lockfile format and `pyproject.toml`, rather than exporting to a
requirements which looses information (which btw. could be implement in
Python inspector).

As a change of the approach seems indicated in the long run, implement
the functionality in a rather minimal invasive way. Also not that the
`--dev` option is actually deprecated.

Signed-off-by: Frank Viernau <[email protected]>