[server] Make connection pooler configurable and set better default values Drop the configuration connections-pool-size and add new configurations options: * connections-pool-min-size. Set to 0 by default so we open connections only when needed. This avoid opening min-size*processes connections at startup, which is, it think, a good default. * connections-pool-max-size. Set to 0 (unlimited) by default, so we move the bottleneck to postgresql. * connections-idle-timeout. Set to 10 minutes. I don't have arguments about this except that this is the default in pgbouncer.

3.26 (1 February 2018)
======================

New features
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* For ``pyramid`` instance configuration kind, logging is not handled anymore
  by CubicWeb but should be configured through ``development.ini`` file
  following https://docs.pylonsproject.org/projects/pyramid/en/latest/narr/logging.html.

Backwards incompatible changes
------------------------------

* CubicWebConfiguration method 'shared_dir' got dropped.