* add CONF_STATE_CLASS to const.py
* move to `sensor/__init__.py`
* move to sensor/const.py
* Revert "move to sensor/const.py"
This reverts commit 604d0d066bfcb93f1a11e3d7732d430ab6de8d59.
* move it to `sensor/const.py` but import it from `sensor/__init__.py`
* add Modbus