Allowed to add custom buttons/widget to grid toolbar.

Add possibility to hide plugin from navigation bar.

core/iplugin.h

@@ -75,6 +75,7 @@ public:
         return (Service<T>*)m_service;
     }
 
+    virtual bool showIcon() { return true; }
     virtual QTranslator* translator() { return NULL; }
     virtual QIcon pluginIcon() { return QIcon(); }
     QMap<QString, QString> translations() { return m_translations; }