CPlusPlus: CppEditor: refactor overview model

Introduce abstract model to be able to use clang
based version of it in follow up patches.
Fix warnings and modernize source code a little.
Move OverviewModel to CppTools.

Change-Id: Idcc9bf03cad047026a456bd01063597a1eb95147
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/cpptools/cppeditoroutline.h

@@ -27,6 +27,8 @@
 
 #include "cpptools_global.h"
 
+#include "abstractoverviewmodel.h"
+
 #include <QModelIndex>
 #include <QObject>
 
@@ -36,7 +38,6 @@ class QSortFilterProxyModel;
 class QTimer;
 QT_END_NAMESPACE
 
-namespace CPlusPlus { class OverviewModel; }
 namespace TextEditor { class TextEditorWidget; }
 namespace Utils { class TreeViewComboBox; }
 
@@ -51,7 +52,7 @@ public:
 
     void update();
 
-    CPlusPlus::OverviewModel *model() const;
+    AbstractOverviewModel *model() const;
     QModelIndex modelIndex();
 
     QWidget *widget() const; // Must be deleted by client.
@@ -79,7 +80,7 @@ private:
     TextEditor::TextEditorWidget *m_editorWidget;
 
     Utils::TreeViewComboBox *m_combo; // Not owned
-    CPlusPlus::OverviewModel *m_model;
+    AbstractOverviewModel *m_model;
     QSortFilterProxyModel *m_proxyModel;
     QModelIndex m_modelIndex;
     QAction *m_sortAction;