Clean up about page (#1282)

* Add InstancePresenter to expose site details

* Clean up about controller, use instance presenter

app/presenters/instance_presenter.rb

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+class InstancePresenter
+  delegate(
+    :closed_registrations_message,
+    :contact_email,
+    :open_registrations,
+    :site_description,
+    :site_extended_description,
+    to: Setting
+  )
+
+  def contact_account
+    Account.find_local(Setting.site_contact_username)
+  end
+
+  def user_count
+    Rails.cache.fetch('user_count') { User.count }
+  end
+
+  def status_count
+    Rails.cache.fetch('local_status_count') { Status.local.count }
+  end
+
+  def domain_count
+    Rails.cache.fetch('distinct_domain_count') { Account.distinct.count(:domain) }
+  end
+end