Test Sidekiq queuing on saving new feed
Add last_checked column/remove is_read
Update Feed callbacks

Add last checked time to feeds to use for scheduling/queuing
Subscribe user after create is run
Add whenever for cron scheduling
Update last_checked on feed when pulling articles
Create whenever schedule

Also add requiring_update scope on Feed to select feeds that haven’t
been updated in the last 20 minutes. Note that you must use `whenever
-i` to update crontab on machine running app.
Add #update_feeds to Feed model
Validate domain on article

Sometimes article’s permalinks do not include domain. This finds the
domain from the parent feed object and prepends it to permalink if it’s
missing.
Add in session_id for subscription testing
Remove is_read from Article factory
Add last_checked to Feed factory
Test for permalink validation