* Make a flatter one level inheritance, with MySensorsLight as parent
with four children, one per light type.
* Break out helper methods. One per plain light, dimmer and RGB/RGBW
children and per update, turn_on and turn_off, nine in total. Put
these in the parent.
* Call the helper methods as needed from the child methods update,
turn_on and turn_off.
* Change name of MySensorsLightLight to MySensorsLightPlain.
* Fix module docstrings according to pep257.
* Change name of color util method from rgb_hex_to_list to
rgb_hex_to_rgb_list.
* Add unit tests for rgb_hex_to_rgb_list.
6e8c79d531