Update group membership for a group call when it changes.

app/src/main/java/org/thoughtcrime/securesms/util/livedata/LiveDataUtil.java

@@ -129,6 +129,25 @@ public final class LiveDataUtil {
     return mediatorLiveData;
   }
 
+  /**
+   * Skip the first {@param skip} emissions before emitting everything else.
+   */
+  public static @NonNull <T> LiveData<T> skip(@NonNull LiveData<T> source, int skip) {
+    return new MediatorLiveData<T>() {
+      int skipsRemaining = skip;
+
+      {
+        addSource(source, value -> {
+          if (skipsRemaining <= 0) {
+            setValue(value);
+          } else {
+            skipsRemaining--;
+          }
+        });
+      }
+    };
+  }
+
   /**
    * After {@param delay} ms after observation, emits a single Object, {@param value}.
    */