QmlProfiler: Disconnect some signals on shutdown

It's a workaround, not a proper solution (as indicated by the
SOFT ASSERT: "d->m_profilerState" in file qmlprofilerruncontrol.cpp,
line 144 triggering) The state manager (and possibly more)
is referenced from potentially running run controls, that are ramped
down after the plugin.

Task-number: QTCREATORBUG-18736
Change-Id: Ia20b168fe640c818276a777e1d23feab0cacd565
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/plugins/qmlprofiler/qmlprofilerplugin.h

@@ -34,6 +34,8 @@
 namespace QmlProfiler {
 namespace Internal {
 
+class QmlProfilerTool;
+
 class QmlProfilerPlugin : public ExtensionSystem::IPlugin
 {
     Q_OBJECT
@@ -47,6 +49,9 @@ public:
     static QmlProfilerSettings *globalSettings();
 
     QList<QObject *> createTestObjects() const override;
+
+private:
+    QmlProfilerTool *m_profilerTool;
 };
 
 } // namespace Internal