CLI: Revert to and update of parse_datetimearg()

An earlier commit ("CLI: take input date format from configuration file,
do not accept time") replaced parse_datetimearg() with parse_datearg()
and eliminated time-of-day from command line date arguments. This made
the full use of filter options impossible.

That earlier commit is reverted and updated. The parse_datearg()
function is replaced by an updated parse_datetimearg() function that

- takes the date format from the configuration file
- accepts date, date-time or time

The updated parse_datetimearg() function has been extended to report
back the type of the date string received in order to set (filter)
options correctly.  Input dates for query ranges (--from, --to, --days)
are still limited to dates only.

Signed-off-by: Lars Henriksen <LarsHenriksen@get2net.dk>
Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

src/ui-calendar.c

@@ -144,6 +144,12 @@ void ui_calendar_set_current_date(void)
 	pthread_mutex_unlock(&date_thread_mutex);
 }
 
+/* Return the current date. */
+struct date *ui_calendar_get_today(void)
+{
+	return &today;
+}
+
 /* Needed to display sunday or monday as the first day of week in calendar. */
 void ui_calendar_set_first_day_of_week(enum wday first_day)
 {