Fix a bug where /jobs?search[name]=Prune+Posts didn't find jobs named PrunePostsJob.
`"Prune Posts".tr(" ", "_").classify` was wrong because it returned `"PrunePost"`.
Fix the /jobs listing to show retried jobs. GoodJob::ActiveJobJob has a
default scope that filters out retried jobs; remove it in the index
controller so we can see retried jobs.
Also fix mail delivery jobs not showing up in the dropdown in the /jobs
search form.
Add ability to search jobs on the /jobs page by job type or by status.
Fixes#2577 (Search filters for delayed jobs). This wasn't possible
before with DelayedJobs because it stored the job data in a YAML string,
which made it difficult to search jobs by type. GoodJobs stores job data
in a JSON object, which is easier to search in Postgres.
