Use the new Sensu libraries, general refactoring

New libraries:
https://github.com/sensu/sensu-logger
https://github.com/sensu/sensu-settings
https://github.com/sensu/sensu-spawn
https://github.com/sensu/sensu-extension
https://github.com/sensu/sensu-extensions

Breaking Sensu apart has made it possible to greatly increase test coverage and general quality.