[table view] some new table view enhancements
* rewrite entiy table view column renderers to use default_* methods instead
of lambda so that column_renderers may be properly deep-copied
* new RelatedEntitiesColRenderer
* default addcount to false on RelatedEntityColRenderer
* more doc
doc/book usr/share/doc/cubicweb-documentation
doc/html usr/share/doc/cubicweb-documentation
debian/cubicweb-doc usr/share/doc-base/cubicweb-doc