Move configuration outside of the scheduler

[marcw]

In the present prototype, configuration is inside the scheduler, which expose an HTTP API. This is fundamentally wrong and a new way of managing the configuration should be made.

Requirements are:

• [x] Read configuration from one a store (in-memory, filesystem, database, another poller instance…)
• [x] Write configuration to the same store
• [ ] Sync (add / remove / pause) checks to the scheduler
• [ ] Expose an interface to receive configuration update (reload configuration, new checks, pause check, remove check) (ie: HTTP, AMQP Consumer, …)