Fix various context menu actions from project managers

The correct pattern is this: The actions in the build menu are supposed
to be for the startup project. They should use the global context and be
manually hidden/shown if the startup project changes.

This fixes a crash on assigning keyboard shortcut to the edit files
context menu action.

The slot connected assumed that the action could only be triggered via
the context menu. By using ProjectTree;:currentProject() the code now
works even if the project tree is not actually focused.

It also fixes that the "Run CMake" action was shown even in the build menu,
even though a non cmake project was the startup project.

Change-Id: I0bb8086d8b1078b4c71c3b5ba9d7f8596757e724
Task-number: QTCREATORBUG-14728
Task-number: QTCREATORBUG-14768
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/genericprojectmanager/genericprojectplugin.h

@@ -50,8 +50,6 @@ class GenericProjectPlugin : public ExtensionSystem::IPlugin
     Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QtCreatorPlugin" FILE "GenericProjectManager.json")
 
 public:
-    GenericProjectPlugin();
-
     bool initialize(const QStringList &arguments, QString *errorString);
     void extensionsInitialized() {}
 
@@ -64,9 +62,6 @@ private slots:
     void test_mixed1();
     void test_mixed2();
 #endif // WITH_TESTS
-
-private:
-    ProjectExplorer::Project *m_contextMenuProject;
 };
 
 } // namespace Internal