[web][s]: guard against no DB backend being available when showing front page.
[web][s]: guard against no DB backend being available when showing front page.

stefanhahmann/pybossa,geotagx/geotagx-pybossa-archive,OpenNewsLabs/pybossa,inteligencia-coletiva-lsd/pybossa,Scifabric/pybossa,jean/pybossa,geotagx/geotagx-pybossa-archive,CulturePlex/pybossa,geotagx/pybossa,CulturePlex/pybossa,OpenNewsLabs/pybossa,proyectos-analizo-info/pybossa-analizo-info,proyectos-analizo-info/pybossa-analizo-info,stefanhahmann/pybossa,geotagx/geotagx-pybossa-archive,harihpr/tweetclickers,Scifabric/pybossa,PyBossa/pybossa,jean/pybossa,harihpr/tweetclickers,inteligencia-coletiva-lsd/pybossa,geotagx/geotagx-pybossa-archive,CulturePlex/pybossa,geotagx/pybossa,geotagx/geotagx-pybossa-archive,proyectos-analizo-info/pybossa-analizo-info,PyBossa/pybossa