* Add profile to json+ld in Accept
It's required by the ActivityPub spec
* Use headers['Content-type'] instead of mime_type
mime_type strips the profile from the content type, but it's still available raw in the headers hash
* Add test for ld+json with profile
* No need to re-require sidekiq plugins, they are required via Gemfile
* Add derailed_benchmarks tool, no need to require TTY gems in Gemfile
* Replace ruby-oembed with FetchOEmbedService
Reduce startup by 45382 allocated objects
* Remove preloaded JSON-LD in favour of caching HTTP responses
Reduce boot RAM by about 6 MiB
* Fix tests
* Fix test suite by stubbing out JSON-LD contexts
Fetching atom extracted from FetchRemoteAccountService and FetchRemoteStatusService
into FetchAtomService. Mentions of the constant "http://activityschema.org/collection/public"
skipped as it's not a real URL/user.
