[dataimport] dispatch and deprecate old code
previously, the whole dataimport.py content has been copied in
dataimport/__init__.py, then dataimport/importer.py API has been introduced.
Following these changes, this cset:
* dispatch __init__ code into sub-modules
* dispatch unittest_dataimport accordingly
* deprecates functions and classes that are deprecated by the new API
Related to #5414753.
The facets system
-----------------
Facets allow to restrict searches according to some user friendly criterias.
CubicWeb has a builtin `facet`_ system to define restrictions `filters`_ really
as easily as possible.
Here is an exemple of the facets rendering picked from our
http://www.cubicweb.org web site:
.. image:: ../../images/facet_overview.png
Facets will appear on each page presenting more than one entity that may be
filtered according to some known criteria.
Base classes for facets
~~~~~~~~~~~~~~~~~~~~~~~
.. automodule:: cubicweb.web.facet
.. _facet: http://en.wikipedia.org/wiki/Faceted_browser
.. _filters: http://www.cubicweb.org/blogentry/154152