Fixes #8838 - Replace HTTP error codes with human-readable symbols

fixes #8484 - make SmartProxyAuth concern more useful to plugins

fixes #8049 - Add timezone to user

fixes #8627 - add host comment field to API documentation

fixes #8228 - add a config_templates concern to serve config_templates controllers

Fixes #8284 - missing params in OS api docs

fixes #8459 - remove sp_subnet_id from api/hosts

Refs #3809 - Remove useless assignments

fixes #7586, #7734, #7172 - user preferences for receiving mail notifications

Adds a framework for user-selectable mail notifications. The work is
still done in ActionMailer classes and launch by rake in cron, however a
wrapper called MailNotification is used to provide RBAC and make the...

fixes #4463 - use unattended URL for hostgroup provisioning