add filter by owner for /forms /data and /projects endpoints

This function body and that of the function starting line 29, are so similar, begging for an abstraction,

```python
def _filter_qs_by(request, queryset, prefix):
    owner = request.QUERY_PARAMS.get('owner')
    
    if owner:
        kwargs = {}
        kwargs[prefix + '__owner'] = owner
        return queryset.filter(**kwargs)

    return queryset

_filter_qs_by(request, queryset, 'user')
```