QmlDebugger: Added dialog "Attach to QML Port..."

The dialog is added to Debug->Start Debugging menu option. It specifies the host
and port that the JSDebugClient connects to for listening to debug messages.

Change-Id: I7f828c169ff2338f4780025f72182c5fc8784c4a
Reviewed-on: http://codereview.qt-project.org/4824
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Kai Koehne <kai.koehne@nokia.com>

src/plugins/debugger/debuggerconstants.h

@@ -126,6 +126,7 @@ enum DebuggerStartMode
     AttachCrashedExternal, // Attach to crashed process by process id
     AttachCore,            // Attach to a core file
     AttachToRemote,        // Start and attach to a remote process
+    AttachToQmlPort,       // Attach to QML debugging port
     StartRemoteGdb,        // Start gdb itself remotely
     StartRemoteEngine      // Start ipc guest engine on other machine
 };