Fail jobs that terminate the process

Jobs that terminate the process still also terminate the worker.php, but now it marks the job as failed, so the worker can move on when it restarts.

Widget for failed jobs

This adds:

• A panel widget! 🎉
• queue::retry($failedJob), to add a failed job back to the queue
• queue::remove($failedJob), to remove a failed job entirely
• [BREAKING] queue::jobs() and queue::failedJobs() now return a Collection instead of an array, so you can use queue::jobs()->first() and all the good stuff
• DocBlocks, cuz yeah