Add GPIO to select display brightness.

[twrackers]

Default (HIGH) selects close to minimum brightness for indoors.
LOW selects maximum brightness for outdoors, especially when sunny.

[twrackers]

Optical sensor not practical, will use GPIO 12 pulled low to set full brightness.

[twrackers]

May eventually convert all GPIO inputs to toggle states w/ debouncing. Then touch sensors or momentary buttons can be used if there's some form of visual feedback (i.e. display or LEDs).