Add the ability to export print template as html

This way we can view the html generated from a print template, for
debugging, validation or printing via your favorite browser.

Signed-off-by: Anton Lundin <glance@acc.umu.se>

desktop-widgets/printer.h

@@ -40,6 +40,7 @@ public:
 	~Printer();
 	void print();
 	void previewOnePage();
+	QString exportHtml();
 
 signals:
 	void progessUpdated(int value);