Correct and improve calendar events updating algorithm.

1. UpdateCalendarService will fetch all events from now to the next fetch time + Preferences.showUntil, so that EventRepository holds all events need to be shown before the next fetch;
2. Every event is updated 1 minute after the corresponding time span, to make the actual time difference consistent with the displayed getRelativeTimeSpanString;
3. Update events only when necessary, eliminate redundant alarms; cancel all update alarms when showEvents is turned off.

app/src/main/java/com/tommasoberlose/anotherwidget/receivers/NewCalendarEventReceiver.kt

@@ -13,8 +13,7 @@ class NewCalendarEventReceiver : BroadcastReceiver() {
     override fun onReceive(context: Context, intent: Intent) {
         val eventRepository = EventRepository(context)
         when (intent.action) {
-            Intent.ACTION_PROVIDER_CHANGED,
-            Intent.ACTION_TIME_CHANGED -> {
+            Intent.ACTION_PROVIDER_CHANGED -> {
                 CalendarHelper.updateEventList(context)
             }
             Actions.ACTION_GO_TO_NEXT_EVENT -> {