Fix #54 - Fetch remote accounts by URL from mentions

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.

spec/services/fetch_atom_service_spec.rb

@@ -0,0 +1,4 @@
+require 'rails_helper'
+
+RSpec.describe FetchAtomService do
+end

spec/services/fetch_feed_service_spec.rb

@@ -1,8 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe FetchFeedService do
-  subject { FetchFeedService.new }
-
-  it 'fetches remote user\'s feed'
-  it 'processes the feed'
-end

spec/services/fetch_remote_account_service_spec.rb

@@ -0,0 +1,4 @@
+require 'rails_helper'
+
+RSpec.describe FetchRemoteAccountService do
+end

spec/services/fetch_remote_status_service_spec.rb

@@ -0,0 +1,4 @@
+require 'rails_helper'
+
+RSpec.describe FetchRemoteStatusService do
+end