Remove unneeded indices, improve error handling in background workers, don't needlessly reload reblogged status, send Devise e-mails asynchronously

silenced mode + edits

From https://github.com/doorkeeper-gem/doorkeeper-i18n/blob/master/rails/locales/fr.yml

From https://gist.github.com/qsypoq/4cf3b858ff8242ffb013

during Fan Out On Write to load less stuff into memory