basic: calendarspec UTC support

Just add " UTC" to the end of the event expression. Works for the
special expressions.

src/basic/calendarspec.h

@@ -36,6 +36,7 @@ typedef struct CalendarComponent {
 
 typedef struct CalendarSpec {
         int weekdays_bits;
+        bool utc;
 
         CalendarComponent *year;
         CalendarComponent *month;