Allow overriding spreadsheet creation.
Allow overriding spreadsheet creation.

BenHeubl/dailygraphics,cerealcommas/mashgraphics,stlpublicradio/dailygraphics,abcnews/dailygraphics,onyxfish/dailygraphics,louisstow/dailygraphics,wjcjenny/dailygraphics,abcnews/dailygraphics,nprapps/dailygraphics,BenHeubl/dailygraphics,stlpublicradio/dailygraphics,wjcjenny/dailygraphics,abcnews/dailygraphics,louisstow/dailygraphics,cerealcommas/mashgraphics,onyxfish/dailygraphics,wjcjenny/dailygraphics,stlpublicradio/dailygraphics,nprapps/dailygraphics,louisstow/dailygraphics,BenHeubl/dailygraphics,cerealcommas/mashgraphics,abcnews/dailygraphics,nprapps/dailygraphics,swastvedt/dailygraphics,eads/dailygraphics,eads/dailygraphics,swastvedt/dailygraphics,stlpublicradio/dailygraphics,nprapps/dailygraphics,swastvedt/dailygraphics,eads/dailygraphics,onyxfish/dailygraphics