* [#260] One click deploy to heroku
* Added app.json file for Heroku deployment
* Made changes in Procfile to accept the PORT as env variable
* Added the one click button in README.md
* Change readme and link
* Alignment of button in Readme
* Changing redis to free plan
* Removed node-js build-pack
* Changed the post-deploy script to be rake db:migrate
* Removed web concurrency variable from app.json for heroku
* Changed the link to chatwoot logo referenced in app.json
* Changed postdeploy hook
* Changed logo to be raw content from github
* Changed the SMTP variables
* Added optional conditional for sending mail
* Changed the naming of SMTP variables
* Having logo as base 64 encoded image for heroku deploy page
* Fixed key not found error for SMTP variables
* Correcting the specs for conversation assignment mailer
* Spec rubocop fixes
* Spec rubocop fixes
* Added the link to master for heroku app.json
