[server] extract "no pooler" CnxSet class to a _BaseCnxSet class So we get rid of "if self._queue is None" in each method of _CnxSetPool Also add helper get_cnxset(source, size) to instantiate the correct pooler class.

.. _appobject_module:

:mod:`cubicweb.appobject`
=========================

.. automodule:: cubicweb.appobject

   .. autoclass:: AppObject
      :show-inheritance:
      :members: