Allow InterceptHandler to specify the messages they can intercept. This allows us to improve the performance of the broker interceptor, and will make log traces more clear.

- Add methods to return an unique identifier and the supported message types at the InterceptHandler interface.
- Include a default implementation of the new methods in the AbstractInterceptHandler. By default, all the interceptors will be able to handle any message (same as before).
- Comment verifyNoMoreInteractions() call from the BrokerInterceptorTest.testAddAndRemoveInterceptHandler(). The removeInterceptHandler() method of the broker interceptor
  polls the InterceptHandler, so an interaction will always exist after the call to onSubscribe().

broker/src/main/java/io/moquette/server/Server.java

@@ -246,11 +246,11 @@ public class Server {
      * @param interceptHandler the handler to add.
      * @return true id operation was successful.
      * */
-    public boolean addInterceptHandler(InterceptHandler interceptHandler) {
+    public void addInterceptHandler(InterceptHandler interceptHandler) {
         if (!m_initialized) {
             throw new IllegalStateException("Can't register interceptors on a server that is not yet started");
         }
-        return m_processor.addInterceptHandler(interceptHandler);
+        m_processor.addInterceptHandler(interceptHandler);
     }
 
     /**
@@ -258,11 +258,11 @@ public class Server {
      * @param interceptHandler the handler to remove.
      * @return true id operation was successful.
      * */
-    public boolean removeInterceptHandler(InterceptHandler interceptHandler) {
+    public void removeInterceptHandler(InterceptHandler interceptHandler) {
         if (!m_initialized) {
             throw new IllegalStateException("Can't deregister interceptors from a server that is not yet started");
         }
-        return m_processor.removeInterceptHandler(interceptHandler);
+        m_processor.removeInterceptHandler(interceptHandler);
     }
 
 }