Renders one or more large picture-background buttons, each firing a JavaScript onclick action.
Button — set as ReportType in def_report.
def Render(self, Param1="", Param2="", Param3="", Orientation="") -> str:
Returns HTML <button> elements. The query must return at least two columns per row: the onclick JavaScript expression (column 1) and the image filename served from /image/ (column 2). Button colour is taken from self._Colour; the button label from self._Title.