Outline: Redo save/restore of settings

The OutlineStackWidget stored its position in the outline to be able
to save/restore settings specific to the sub-widget (IOutlineWidget).
However, the index can get out sync if another NavigationWidget
with a lower index number is split, and the relative position changes.

The change therefore avoids saving an index, and rather keeps the sum
of all sub-widget settings in a QVariantMap, only reading and writing
to the global settings object if necessary.

The settings are also not stored in the [General] section anymore,
but in a subgroup [Sidebar.Outline.X], where X is the index of the
outline in the view. This avoids having to always iterate over all
keys. No effort has been made to take over the old settings. I doubt
anyone will notice, though.

Change-Id: I85017cbb3e32b0a16da43ce6339deb7a053d6b09
Task-number: QTCREATORBUG-13614
Reviewed-by: Daniel Teske <daniel.teske@theqtcompany.com>

src/plugins/qmljseditor/qmljsoutline.h

@@ -74,8 +74,8 @@ public:
     // IOutlineWidget
     virtual QList<QAction*> filterMenuActions() const;
     virtual void setCursorSynchronization(bool syncWithCursor);
-    virtual void restoreSettings(int position);
-    virtual void saveSettings(int position);
+    virtual void restoreSettings(const QVariantMap &map);
+    virtual QVariantMap settings() const;
 
 private slots:
     void modelUpdated();