[cubicweb/doc] Add tutorial on data import in CubicWeb. This involves creating the "tutorials/dataimport" directory structure under "cubicweb/doc" and, inside the "dataimport" directory, putting several files: - a ResT file containing the tutorial *per se*; this tutorial addresses the following issues: * creating a CubicWeb schema for representing a given data set (here, the Diseasome RDF data, for illustration purposes); * parsing the data; * importing the data, by using several stores: + the ``RQLObjectStore``, ``NoHookRQLObjectStore`` and ``SQLGenObjectStore`` from the ``dataimport`` module in CubicWeb; + the ``MassiveObjectStore`` from the ``dataimport`` module in the ``dataio`` cube. The tutorial also provides timing benchmarks of the various stores. - a set of Python files illustrating the data import, in the context of Diseasome RDF data parsing: * a Diseasome RDF data parse module, * a Diseasome data import module, * a CubicWeb schema for representing Diseasome data.

for eschema in schema.entities():
    if not (eschema.final or 'cw_source' in eschema.subjrels):
        add_relation_definition(eschema.type, 'cw_source', 'CWSource', ask_confirm=False)

sql('INSERT INTO cw_source_relation(eid_from, eid_to) '
    'SELECT e.eid,s.cw_eid FROM entities as e, cw_CWSource as s '
    'WHERE s.cw_name=e.source AND NOT EXISTS(SELECT 1 FROM cw_source_relation WHERE eid_from=e.eid AND eid_to=s.cw_eid)')
commit()