Show starting live location beacons as location delegates in the timeline

Also, hide ending live location beacon state changes.

src/models/messageeventmodel.h

@@ -53,6 +53,7 @@ public:
         ReadMarker, /**< The local user read marker. */
         Poll, /**< The initial event for a poll. */
         Location, /**< A location event. */
+        LiveLocation, /**< The initial event of a shared live location (i.e., the place where this is supposed to be shown in the timeline). */
         Other, /**< Anything that cannot be classified as another type. */
     };
     Q_ENUM(DelegateType);