change the Excel class so that it’s capable of rendering an empty spreadsheet, instead of barfing a 500 error!

also add the isAuthorized function to the controller…
restyle & rename some CSS classes
removed isAuthorized, removed message in Excel export, and left a comment about the logo
removed an inaccurate comment
Merge pull request #19 from ianring/empty-excel-output

Bugfix: error when excel export had no data