REST API should not be based on Hybrid properties

[szoupanos]

Currently REST API is based on hybrid properties like the user_email defined in the DbNode table in SQLA.

This allows us to create queries where we may project node properties and also the user_email and implicitly to do the join of the DbNode with the DbUser to provide the user email.

This is a nice feature but it is a feature that it is defined at the SQLA model (not in the Django model) and we should not make assumptions that such feature exist at the REST API which is a few levels above the backends.

In general the REST API queries should change from

qh = {'project': {
    'calculations': ['id', 'label', 'node_type', 'ctime', 'mtime', 'uuid', 'user_id', 'user_email',
                     'attributes', 'extras']},
      'path': [{'tag': 'calculations', 'entity_type': 'process.calculation.calcjob.CalcJobNode.'}],
      'order_by': {'calculations': {}}, 'filters': {}}

to

qh = {
    'project':
        {
            'calc': ['id', 'label', 'node_type', 'ctime', 'mtime', 'uuid', 'user_id', 'attributes', 'extras'],
            'user_1': ['email']
        },
    'path':
        [
            {'entity_type': 'process.calculation.calcjob.CalcJobNode.', 'tag': 'calc'},
            {'edge_tag': 'calc--user_1', 'joining_keyword': 'with_node', 'entity_type': 'user',
             'joining_value': 'calc', 'tag': 'user_1'}
    ],
    'order_by': {'calc': {}}

This issue became visible after the removal of the dummy_model (for the querying of Django backrend). Work which is done to support JSONB in Djnago