Job Scheduler Bundle

This is the job scheduler bundle we discussed about a few days ago.

| Q             | A
| ------------- | ---
| Bug fix?      | [no]
| New feature?  | [yes]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [yes]
| Fixed tickets | []
| License       | MIT
| Doc PR        | []

job.enabled.priority.feature test might fail, but I couldn't think of any other way to test priority....maybe with phpspec?

Some resources and assetic configuration are defined in config.yml, maybe they should be moved to WebBundle?