Features

• Adding new mj-preview tag in mj-head to set an email preview that will be displayed in email clients but hidden from the body of the email (cf https://litmus.com/blog/the-ultimate-guide-to-preview-text-support)
• Revert "fully clickable" button because of incompatibility in several email clients

Fixes

• mj-text now only adds the class on the root tr when using css-class
• MJML-Validator should no longer return a validation error about css-class being invalid