core: use a class derived from QList<int> instead of a QList<int> for Core::Context

A mostly mechanical change.

Reviewed-By: con

src/plugins/coreplugin/editmode.h

@@ -58,7 +58,7 @@ public:
     int priority() const;
     QWidget* widget();
     QString id() const;
-    QList<int> context() const;
+    Context context() const;
 
 private slots:
     void grabEditorManager(Core::IMode *mode);