ui-day: Large-scale refactoring

Use the generic list box implementation for the appointments panel. This
results in some major changes to how the items are printed.

Note that this temporarily removes the heading showing the POM and the
date as well as the separating line between events and appointments.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/args.c

@@ -307,7 +307,9 @@ app_arg(int add_line, struct date *day, long date, const char *fmt_apt,
 	if (date == 0)
 		date = get_sec_date(*day);
 
-	int n = day_store_items(date, NULL, NULL, regex);
+	day_store_items(date, regex);
+
+	int n = day_item_count();
 
 	if (n > 0) {
 		if (add_line)