Adding Sidekiq for background processing (firstly just of mailers)

config/initializers/sidekiq.rb

@@ -0,0 +1,11 @@
+redis_conn = proc {
+  $redis.dup
+}
+
+Sidekiq.configure_server do |config|
+  config.redis = ConnectionPool.new(size: 5, &redis_conn)
+end
+
+Sidekiq.configure_client do |config|
+  config.redis = ConnectionPool.new(size: 25, &redis_conn)
+end