Merge pull request #483 from telerik/Aleks/implement-displayModeChanged-event

Implemented event that invokes on display mode changed.

Author: APopatanasov

Controls/Input/Input.UWP/Calendar/View/RadCalendar.cs

@@ -440,6 +440,11 @@ public event EventHandler<CurrentSelectionChangedEventArgs> SelectionChanged
             }
         }
 
+        /// <summary>
+        /// Occurs when the <see cref="DisplayMode"/> property is changed.
+        /// </summary>
+        public event EventHandler<EventArgs> DisplayModeChanged;
+
         /// <summary>
         /// Gets the <see cref="CommandService"/> instance that manages the commanding behavior of this instance.
         /// </summary>
@@ -2681,6 +2686,8 @@ private static void OnDisplayModePropertyChanged(DependencyObject target, Depend
                 calendar.FetchNewAppointments();
                 calendar.model.multiDayViewModel.updateFlag = MultiDayViewUpdateFlag.All;
             }
+
+            calendar.DisplayModeChanged?.Invoke(calendar, new EventArgs());
         }
 
         private static void OnCalendarViewHeaderFormatPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)