Don't include empty query parameter in URLs
Don't include empty query parameter in URLs

The spreadsheets API endpoint returns an HTTP 400 error with a
message of "Invalid query parameter value for sq." when the
``sq`` query parameter is empty.  The default case for Tabletop
is an empty query.  Only add the ``sq`` parameter to the generated
URL if ``this.query`` is not empty.

Addresses https://github.com/jsoma/tabletop/issues/45

Faiz7412/tabletop,Faiz7412/tabletop,POWERWEBDESIGN/tabletop,jsoma/tabletop,jsoma/tabletop,AlmirKadric/tabletop,airtonix/tabletop,POWERWEBDESIGN/tabletop,AlmirKadric/tabletop,ohio813/tabletop,POWERWEBDESIGN/tabletop,airtonix/tabletop,yiakwy/tabletop,aendrew/tabletop,knmurphy/tabletop,knmurphy/tabletop,Faiz7412/tabletop,POWERWEBDESIGN/tabletop,muhanadra/tabletop,RachBLondon/tabletop,aendrew/tabletop,muhanadra/tabletop,muhanadra/tabletop,knmurphy/tabletop,aendrew/tabletop,yiakwy/tabletop,Faiz7412/tabletop,yiakwy/tabletop,airtonix/tabletop,RachBLondon/tabletop,ohio813/tabletop,AlmirKadric/tabletop,greyhwndz/tabletop,aendrew/tabletop,greyhwndz/tabletop,jsoma/tabletop,yiakwy/tabletop,RachBLondon/tabletop,ohio813/tabletop,knmurphy/tabletop,greyhwndz/tabletop