Send welcome mail upon successful signup. #13

Setup the backend to send a welcome mail to a user on successfully signing up.

Acceptance criteria

• Module that allows application should be able to send a rich text email on signing up
• Application should use an external template for the mail which gets updated with user's details.
• Should be able to embed images in the email.
• Easily updatable template.
• Documentation on how to use the module including any authentication details etc. DO NOT CHECK IN SENSITIVE KEYS
• Preferably don't integrate with a campaign service just yet.

Bonus

• Include details if we are able to avoid SPAM filters.
• It can be used for sending verification mails for signups using email.