Time, date, and setup menu (2017-11-18)

Time and date viewing and setting are implemented here, as well as the setup menu (though only the first 4 options have effect). The settings are stored in EEPROM – on first run, hold the Select button during startup, and it will write the defaults into EEPROM (every write to EEPROM is written to the serial console as well).

Very glad this works, but no idea whether this is ultimately a better approach than the original code, which was organized primarily by clock function (time, date, etc) whereas this is more of a "control first" approach, where the methods are for handling inputs, setting values, updating the display, etc. I think it makes sense when user experience patterns are shared across multiple functions... but there is a bit more overhead. Perhaps this is what happens when a web developer has a go at embedded programming!