Settings should have a way to edit system date and time

[truedat101]

Because the Espressobin doesn't have a clock, we can't store the time. And because devices might move around, you should have a way to edit the date and time.

• todo: figure out right date format
• add ui to display date and time in an editable field (validate input)
• add ui to display timezone as well in an editable field. (validate input - string input only)
• implement system exec() stubs for the above two if fields are edited.