Add settings to enable 24-hour time format and customizable date format (#2347)

Add settings to enable 24-hour time format and customizable date format (#2347)

* Add setting to enable 24-hour time format

* added hour24Clock to TimeProps

* Add incomplete dateFormatString setting

* Move 24-hour  toggle to Appearance

* Add "Date & Time" subheading, cleanup after merge

* Add setting for date formatting

* Fix minor formatting and naming issues

* Document functions

* adress most comments

* add hint for date formatting

* add support for 24hr time to TimePicker

* prevent overflow on small displays