Send emails via sidekiq (#380)

* add sidekiq web view if the user is an administrator

* add sidekiq setup configuration and support

* update devise to use delivery_later method and update test

* update conversation to use deliver_later instead of deliver

* Update Routes

* Add Procfile for Heroku One-Click Start

* updating docs

* update concurrency and Procfile for supporting Heroku Free Dyno

* update Procfile.dev

app/models/user.rb

@@ -86,6 +86,10 @@ class User < ApplicationRecord
   after_create :notify_creation
   after_destroy :notify_deletion
 
+  def send_devise_notification(notification, *args)
+    devise_mailer.send(notification, self, *args).deliver_later
+  end
+
   def set_password_and_uid
     self.uid = email
   end