* Make default constructor for touch calibration
* Add persistent memory check value and access abstraction.
* Add persistent data_t default constructor with reasonable defaults.
* serial_format_t default constructor.
* Tidy up backlight timeout type.
* Add persistent data struct version/checking.
* Make range_t functions constexpr.
* Move ui_config and functions into class.
* Add backlight_config_t struct, separate enable and time settings.
