Pass the correct arguments when enqueuing a SubscribeUserJob.

A job_status_id arg was added to SubscribeUserJob.perform, but the new arg was not being passed when enqueuing the job from URLSubscriber.enqueue_subscribe_job
Added controller and routes to operate on SubscribeJobState instances from the client.
WIP: display the state of subscribe jobs in the start page.
Changed icon while a subscribe job is running. Put the partial for the import process status in the same folder as the partials that paint other kinds of job state alerts.
The FeedsController#create action returns just an HTTP 200 header.

With the change to performing subscriptions in a background job, it makes no sense to return a JSON document describing the subscribed feed.
Show the alerts in the start page when there are subscribe job alerts, but no refresh feed job alerts.
Fixed closing of subscribe alerts in the start page.

Remember kids: in coffeescript, indentation is NOT your friend! Also, a function to find a specific subscribe_job_state object in coffeescript was being invoked with the wrong name.
Minor change in i18n strings for subscribe job state alerts.