Editors: Support dragging from outline views

Fill the line and column information in the location returned by
QmlOutlineModel::sourceLocation for that.
The drag & drop code also needed a way to override the executed drop
action for file drops, because the QML outline supports move-drags, which
would lead to the items being removed from the outline when dragged onto
a split...

Change-Id: I2478abc7d5aa2f3aa676cdd609ecb69a50adce8c
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@digia.com>

src/plugins/cppeditor/cppoutline.h

@@ -60,6 +60,7 @@ public:
     // QSortFilterProxyModel
     bool filterAcceptsRow(int sourceRow,
                           const QModelIndex &sourceParent) const;
+    Qt::DropActions supportedDragActions() const;
 private:
     CPlusPlus::OverviewModel *m_sourceModel;
 };