Handle errors creating Watchtower subscriptions #105
Description
From discussion in #indieweb-dev.
Some feeds that I had recently added to my self-hosted copy of Aperture appeared to subscribe successfully, but stayed at 0 entries. I looked in my (self-hosted) Watchtower DB and couldn't find the subscriptions there.
After some testing and checking of logs, I found that the HTTP endpoint for my Watchtower setup was incorrect and returning 502s. However, Aperture gave no indication that there was an issue creating the subscription.