* Add backlight handling for lcd_pcf8574
Switch the backlight on or off by calling id(mydisplay).backlight()
or id(mydisplay).no_backlight() in lamda functions (assuming mydisplay
is the custom id for the LCD).
* Use abstract method
Co-authored-by: Attila Darazs <attila@darazs.com>
Co-authored-by: Otto Winter <otto@otto-winter.com>
