Add user locales.
Add user locales.

This commit checks first the user preferred language from the browser. Then
it checks for the language Cookie. If the cookie is empty, the user language is
used, otherwise the cookie one.

PyBossa/pybossa,Scifabric/pybossa,geotagx/pybossa,PyBossa/pybossa,geotagx/pybossa,Scifabric/pybossa