fixes #8484 - make SmartProxyAuth concern more useful to plugins

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 #7994 - increased default token_duration setting

fixes #7657 - remove default OAuth credentials

Fixes #2283 , #3135 - add config option for proxy_request_timeout

Refs #4611 - rake-ify foreman-config and db_pending_migration/seed in settings

This way, we can determine in the installer if the rake
db:migrate/seed should be run in the installer.

Later, we also could use this information to inform the entering user
that the application is not in ready state yet: preparation for...

Fixes #3840 - Removes unused Signo related code

fixes #3601: Use secure websockets if available

Websockets_ssl* settings must be configured with the appropriate
certificates for this to work.

fixes #5105 - remove Setting['remove_classes_not_in_environment']