Changed some install instructions. Fixes #722
Changed some install instructions. Fixes #722

Use username pybossa as default (the same as in vagrant).
Minimum requirement Python 2.7.2 because of a date bug.
Use defaults for `createuser` except that user pybossa can also create DBs.

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