[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.

CSS Coding Standards
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(Draft, to be continued)

:Naming: camelCase

Indentation rules
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- 2 espaces avant les propriétés

- pas d'espace avant les ":", un espace après

- 1 seul espace entre les différentes valeurs pour une même propriété


Documentation
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Please keep rules semantically linked grouped together, with a comment about
what they are for.

Recommendation
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- Try to use existing classes rather than introduce new ones

- Keep things as simple as possible while in the framework

- Think about later customization by application

- Avoid introducing a new CSS file for a few lines of CSS, at least while the
  framework doesn't include packing functionalities