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-tests/src/org/briarproject/clients/MessageTreeTest.java

@@ -86,6 +86,16 @@ public class MessageTreeTest {
 			return parentId;
 		}
 
+		@Override
+		public void setLevel(int level) {
+
+		}
+
+		@Override
+		public void setDescendantCount(int descendantCount) {
+
+		}
+
 		@Override
 		public long getTimestamp() {
 			return timestamp;