Plugwise

- Initial support for Stretch (v2/v3) including tests
- Force gzip encoding, work-around for aiohttp-error
- Improve P1 DSMR legacy support
- Ensure `gateway_id` is properly defined (i.e. not `None`)
- b4: Use `domain_objects` over `direct_objects` endpoints
- Remove py3x internal modules (as requested per 86)
- CI-handling improvements and both 3.7 and 3.8 testing
- Code cleanup and output formatting improvements

- Fix situation where `unique_id` was set to `None` for legacy P1 DSMRs
- Introduce using the (discovered) hostname as unique_id

- Registered node counter
- Improved reliability of node discovery
- Fixed negative power usage

alpha - rewrite to async

Change log former Smile