ClangTools: Polish ClangDiagnosticConfigsWidget

* Improve distinction between built-in and custom configs by introducing
  corresponding parent nodes
* Add button to rename a config
* Make closing the dialog apply the selected config.
* Adapt also the related ClangDiagnosticConfigsSelectionWidget showing a
  combo box of the diagnostic configs and a "Manage..." button: Remove
  the combo box and show the current config as the button text.

Change-Id: Ic015df37f2532f84bd7da6cd20bfce07799a97b8
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/clangcodemodel/clangprojectsettingswidget.h

@@ -44,7 +44,6 @@ public:
     explicit ClangProjectSettingsWidget(ProjectExplorer::Project *project);
 
 private:
-    void onCurrentWarningConfigChanged(const Core::Id &currentConfigId);
     void onDelayedTemplateParseClicked(bool);
     void onGlobalCustomChanged(int index);
     void onAboutToSaveProjectSettings();
@@ -53,8 +52,6 @@ private:
     void syncGlobalCustomComboBox();
     void syncOtherWidgetsToComboBox();
 
-    void refreshDiagnosticConfigsWidgetFromSettings();
-
 private:
     Ui::ClangProjectSettingsWidget m_ui;
     ClangProjectSettings &m_projectSettings;