Add smack-websocket-java11

This also lifts a bunch of logic from smack-websocket-okhttp into
smack-websocket. Furthermore, the following subprojects require now
Java 11:
- smack-integration-test
- smack-omemo-signal-integration-test
- smack-repl
- smack-websocket-java11

Related tracking issue: SMACK-835

smack-tcp/src/main/java/org/jivesoftware/smack/tcp/XmppTcpTransportModule.java

@@ -664,7 +664,6 @@ public class XmppTcpTransportModule extends ModularXmppClientToServerConnectionM
             return tlsState.engine.getSession();
         }
 
-        @Override
         public boolean isConnected() {
             SocketChannel socketChannel = XmppTcpTransportModule.this.socketChannel;
             if (socketChannel == null) {