Add PHP-FPM tuning parameters

This changeset adds performance-tuning parameters for PHP.

It parameterizes various performance settings for PHP-FPM pools, allowing them to be defined per-environment.  There are good defaults for development, so nothing has to be done to upgrade in development.

It also adds a call to the restart handler for PHP when other PHP config files are updated.

The existing Wordpress restart handler has been fine-tuned to reload PHP-FPM rather than stop and start it.