Improve prefetch by the Project model

class PrefetchManager(models.Manager):
    def get_queryset(self):
        from onadata.apps.logger.models.xform import XForm
        from onadata.apps.api.models.team import Team
        return super(PrefetchManager, self).get_queryset().select_related(
            'created_by', 'organization'
        ).prefetch_related(
            Prefetch('xform_set',
                     queryset=XForm.objects.filter(deleted_at__isnull=True)
                     .select_related('user')
                     .prefetch_related('user')
                     .prefetch_related('dataview_set')
                     .prefetch_related('metadata_set')
                     .only('id', 'user', 'project', 'title', 'date_created',
                           'last_submission_time', 'num_of_submissions',
                           'downloadable', 'id_string', 'is_merged_dataset'),
                     to_attr='xforms_prefetch')

The above prefetch code will cause serious memory issues when dealing with a project that has a lot of dataviews.

In the case of one user who had over 400,000 dataviews in one project, she was never able to load the projects endpoint for that specific project as the onadata application would always get OOM killed.