Merge branch '556-thread-safety-blocking-issues' into 'master'

Forum controller thread safety and tree safety

This branch solves the concurrent forum issues by code restructure and refactoring.

Closes #556 
Closes #552 

See merge request !262

briar-android/src/org/briarproject/android/util/NestedTreeList.java

@@ -0,0 +1,51 @@
+package org.briarproject.android.util;
+
+import android.support.annotation.UiThread;
+
+import org.briarproject.api.clients.MessageTree;
+import org.briarproject.clients.MessageTreeImpl;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.List;
+
+@UiThread
+public class NestedTreeList<T extends MessageTree.MessageNode>
+		implements Iterable<T> {
+
+	private final MessageTree<T> tree = new MessageTreeImpl<>();
+	private List<T> depthFirstCollection = new ArrayList<>();
+
+	public void addAll(Collection<T> collection) {
+		tree.add(collection);
+		depthFirstCollection = new ArrayList<>(tree.depthFirstOrder());
+	}
+
+	public void add(T elem) {
+		tree.add(elem);
+		depthFirstCollection = new ArrayList<>(tree.depthFirstOrder());
+	}
+
+	public void clear() {
+		tree.clear();
+		depthFirstCollection.clear();
+	}
+
+	public T get(int index) {
+		return depthFirstCollection.get(index);
+	}
+
+	public int indexOf(T elem) {
+		return depthFirstCollection.indexOf(elem);
+	}
+
+	public int size() {
+		return depthFirstCollection.size();
+	}
+
+	@Override
+	public Iterator<T> iterator() {
+		return depthFirstCollection.iterator();
+	}
+}