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

config/routes.rb

@@ -90,6 +90,12 @@ Rails.application.routes.draw do
     end
   end
 
+  # Sidekiq Web UI
+  require 'sidekiq/web'
+  authenticate :user, lambda { |u| u.administrator? } do
+    mount Sidekiq::Web => '/sidekiq'
+  end
+
   # Used in mailer templates
   resource :app, only: [:index] do
     resources :conversations, only: [:show]