We need clearly defined, clean and forward-compatible replications API

We currently have separate and advertised call for creating replications.

But we rely on some already broken view to get replications with their status and we rely on explicit DELETE using couch-style call.

We need to do better.

We have tasks API that will provide us status potentially including error messages.

We need a way to list defined replications (perhaps tasks can do that too, why not, given replications are supposed to be always active). And we need a clear API to DELETE them.