Add SVG multi export

Add a second SVG export option that allows for exporting
a series of icons of various size in one go. A dialog is shown
that allows for entering a file name pattern with place holders
and a list of sizes.

Change-Id: Ic644a9d402aa44af5899c29cf83051fdd7bba3d1
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: Diana de Sousa <diana.desousa@theqtcompany.com>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/imageviewer/exportdialog.h

@@ -34,6 +34,8 @@ namespace Utils { class PathChooser; }
 namespace ImageViewer {
 namespace Internal {
 
+struct ExportData;
+
 class ExportDialog : public QDialog
 {
     Q_OBJECT
@@ -46,8 +48,12 @@ public:
     QString exportFileName() const;
     void setExportFileName(const QString &);
 
+    ExportData exportData() const;
+
     void accept() override;
 
+    static QString imageNameFilterString();
+
 private:
     void resetExportSize();
     void exportWidthChanged(int width);