* Add helper method to return Setting.site_title

* Use site_title helper in application layout

* Use site_title value for og:site_name

* Rewrite Atom generation from stream entries to use Ox instead of Nokogiri::Builder

StreamEntry is now limited to only statuses, which allows some optimization. Removed
extra queries on AccountsController#show. AtomSerializer instead of AtomBuilderHelper
used in AccountsController#show, StreamEntriesController#show, StreamEntryRenderer
and PubSubHubbub::DistributionWorker

PubSubHubbub::DistributionWorker moves n+1 DomainBlock query to PubSubHubbub::DeliveryWorker
instead.

All Salmon slaps that aren't based on StreamEntry still use AtomBuilderHelper and Nokogiri

* All Salmon slaps now use Ox instead of Nokogiri. No touch from status on account

h-feed, h-card and h-entry

removing web app capability from non-webapp pages

for avatars/headers, resize avatars down to 120x120 instead of 300x300. Set cache headers on S3 stuff, also
make it private (aka only accessible via expiring links to prevent hotlinking)

from accounts/tags because it's a terribly inefficient way to paginate
large sets of data

as well as formatting of content

(But there are no Atom feed pagination elements yet)

simplify FanOutOnWriteService, add /api/accounts/lookup method

fix tests (the recorded Salmon fixture expects LOCAL_DOMAIN to be something
specific unfortunately)