Improve error handling of editing/deleting feeds when Superfeeder can't be reached

[calebsmith]

If Superfeeder is down or the site is behind basic-auth, the edit and delete feed views in the aggregator app fail and return a 500 response.

These pages are only viewed by feed-approvers, so the UX doesn't seem mission critical to me at this point, but a more helpful error message would be nice in the long run, especially if the Superfeeder service is down. Also, I assume the staging site will always be under basic-auth. Something along the lines of "The Superfeeder service could not be reached to process this request" seems appropriate.

Thanks for the feedback @necaris

[daaray]

As a 'normal' End User, I can delete the feeds I previously submitted through the front end. This is default functionality brought in from the aggregator app. May be worth considering when determining when to schedule making this modification.