[#139] Send conversation emails (#442)

* [#139] Delayed emails for conversations

* Added the setex and get methods to Redis wrapper
* Set the priorities for the sidekiq queues
* Was not able to use mailhog for testing email in local, switched back to letter opener and added comments on using the SMTP settings
* Added after create hood in messages to queue the sending of mail after 2 minutes using sidekiq worker and also set the redis key for the conversation to avoid the email sending for every message
* Added the sidekiq worker to send the email and delete the conversation redis key
* Added the mailer and mail template
* mailer sends the last 10 messages along with the new messages from the time it was queued

* Send email only in development or if smtp config is set

* Send email only in development or if smtp config is set
* Set the SMTP_PORT in production variable

* Adding redis to circle CI

* Specs for the conversation email changes

* Added specs for conversation email sidekiq worker
* Added specs for conversation mailer
* Added specs in message model for the after create hook for notify email

* Send emails only when there is a reply from agent

* set development to use mailhog

* Adding comments for using letter opener

lib/redis/alfred.rb

@@ -1,4 +1,6 @@
 module Redis::Alfred
+  CONVERSATION_MAILER_KEY = 'CONVERSATION::%d'.freeze
+
   class << self
     def rpoplpush(source, destination)
       $alfred.rpoplpush(source, destination)
@@ -15,5 +17,13 @@ module Redis::Alfred
     def lrem(key, value, count = 0)
       $alfred.lrem(key, count, value)
     end
+
+    def setex(key, value, expiry = 1.day)
+      $alfred.setex(key, expiry, value)
+    end
+
+    def get(key)
+      $alfred.get(key)
+    end
   end
 end