[entities] cw_rest_attr_info() should only consider required attributes (closes #3766717)
This prevents CW from choosing unique but non-required attributes. None/NULL is
a poor choice for RESTful URIs.
Data model
==========
This chapter describes how you define a schema and how to make it evolves as the time goes.
.. toctree::
:maxdepth: 1
definition
metadata
baseschema
define-workflows