Merge branch 'release/0.4.0' into develop
Merge branch 'hotfix/0.4.1' into develop
gem mailgun.
Model model_mailer.
Add welcome mail.
Config mailgun.
Config devise mailer.
Add debounce for button 'signup'.
User after_create send welcome.
bundle update.
Bump version.
Merge branch 'release/0.4.2'