Initialize value for datetime control based on available
data, and keep up-to-date with changes from UI. Supports
clocks/timers, which use datetime as an entry field,
WTD-1221.
Don't force date-time inputs to act as if they are
required; allow them to be treated as optional, but
enforce that this only occurs when left completely
empty (as opposed to partially complete.)
Supports WTD-1221.
Implement date time controls up to the point that
they validate, and information (albeit not the right
information) propagates back up to the containing
form. WTD-530.
