Semi-large rewrite.

* Use Pebbles::River for all queuing. This removes some configuration options and simplifies things like error handling.

* Use Pebbles::River::DaemonHelper to run the daemon. Again, this eliminates some configuration options. Config file is now always config/tootsie.conf, the logging is always done through LOGGER, and the pid file and worker count is specified when running bin/tootsie.

* Retooled logging and notifications. Job notifications are now named tootsie.[event]. There is a config option to use the name "tootsie_completed" for completion events.

* Added support for a dedicated failure queue, with an optional TTL setting.