Project fields

[jochenklar]

This is an experimental PR to see how we can include questions/attributes/values in the main projects table. It works pretty good. The setup expects:

PROJECT_FIELDS = {
    'text': 'http://example.com/terms/questions/catalog/individual/text/text',
    'textarea': 'http://example.com/terms/questions/catalog/individual/textarea/textarea'
}

where the URIs are Questions and the keys label the annotations to the queryset and are also the keys in the project(s) JSON.