Added route and controller action to destroy instances of RefreshFeedJobStatus.
When the user clicks on the "X" button in a refresh job alert, the alert is closed and an HTTP DELETE is sent to delete the job status from the DB.
When the user clicks on the feed link inside a job status alert, the alert is permanently dismissed (as well as loading the feed's entries for the user to read).
Changed i18n string for better coherence.
The job status alerts are ordered by their start times, in reverse order.
Renamed the angularjs hash that contains alert timers in the root scope, to clear the way before implementing other similar hashes for different timers.
While a refresh feed job is running, there is a single timer refreshing its status every 5 seconds, no matter how many times the "start" link in the sidebar is clicked.
When a job status alert is dismissed, if there's a running timer updating that job status, cancel it.

After dismissing an alert, it makes no sense to keep updating that job status.
Added nested route and controller action to retrieve entries in a feed like this: "/feeds/:feed_id/entries.json" and entries in a folder like this: "/folders/:folder_id/entries.json". The special :folder_id value "ALL" is supported, and it means "retrieve all entries from all subscribed feeds". The "include_read" parameter is also supported, and its "true"/"false" value controls whether to return all entries, or only unread entries.

This is intended to replace the current FeedsController#index and FoldersController#index actions. These actions in the future will just return a JSON document describing a single feed or folder, instead of a list of entries.