Followers-only post federation (#2111)

* Make private toots get PuSHed to subscription URLs that belong to domains where you have approved followers

* Authorized followers controller, stub for bulk action

* Soft block in the background

* Add simple test for new controller

* Rename Settings::FollowersController to Settings::FollowerDomainsController, paginate results,
rename "private" post setting to "followers-only", fix pagination style, improve post privacy
preferences style, improve warning style

* Extract compose form warnings into own container, show warning when posting to followers-only with unlocked account

app/controllers/settings/follower_domains_controller.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+class Settings::FollowerDomainsController < ApplicationController
+  layout 'admin'
+
+  before_action :authenticate_user!
+
+  def show
+    @account = current_account
+    @domains = current_account.followers.reorder(nil).group('accounts.domain').select('accounts.domain, count(accounts.id) as accounts_from_domain').page(params[:page]).per(10)
+  end
+
+  def update
+    domains = bulk_params[:select] || []
+
+    domains.each do |domain|
+      SoftBlockDomainFollowersWorker.perform_async(current_account.id, domain)
+    end
+
+    redirect_to settings_follower_domains_path, notice: I18n.t('followers.success', count: domains.size)
+  end
+
+  private
+
+  def bulk_params
+    params.permit(select: [])
+  end
+end