widget: date picker
We need something that is able to select dates with variable precision (day, hour, millisecond).
- Date input (day precision, returns shortened ISO8601 string)
- DateTime input (millisecond precision)
- DateTime input with timezone override
- Date range input
- DateTime range input
Given the complexity of the latter two of these, this will probably involve building higher-order components out of a simpler base UI. Some possibilities: