* Improve error handling on LinkCrawlWorker

* Ignore TimeoutError and InvalidURIError too
* Record errors to debug log
* Enable dead job queue on LinkCrawlWorker

Since most of acceptable errors were already ignored, only our side issue should go to dead job queue.

* Ignore all http gem errors

must be added to the Sidekiq invokation in your systemd file

The pull queue will handle link crawling, thread resolving, and OStatus
processing. Such tasks are more likely to hang for a longer time (due to
network requests) so it is more sensible to not make the "in-house" tasks
wait for them.

since that is only ever called in the background

DistributionWorker. That isn't the heaviest service, yet, but gotta start
somewhere