Add Job Maintanance API

As already discussed in issues, many need to remove, requeue, drop, ... jobs in their production environment. Kue can't decide when or how to do them for you, but it can give you the tools by which you can compose your maintenance scripts.
The list contains:
- Removing old (older than `X` minutes) jobs in `complete`. `failed`
- Fix invalid job indexes. `job`XYZ`doesn't exist` errors
- Re-queue stuck jobs. (how is stuck defined?) Can it be an specific job id? Can it be specific job types older than `X` minutes in `active`? but, when job heartbeats is implemented, it can be done automatically by Kue! (https://github.com/LearnBoost/kue/pull/233)

Start by reviewing the proposed maintenance operations in this issue and the linked heartbeat pull request #233. The scope still needs to define which operations, job states, age filters, job types, and individual job IDs are supported, along with how stuck jobs are identified. Done would require an agreed API and corresponding implementation and tests, but no concrete entry point is named.

Written by the indexing model from the issue text.