Show virtualUser in unread email notifications (and flair)

Show virtualUser in unread email notifications instead of bridging user.

Fix #2621 (closed)

Avatars don't work on local dev:

Dev notes

Other MR's where we touched emails:

• env!27 (merged)

---

• build-scripts/mandrill-templates/unread-notification.html
• The email content: modules/mailer/templates/unread_notification_html.hbs
• The email template: lib/mailers/legacy_mandrill_templates/unread-notification_html.hbs
• public/js/views/chat/tmpl/chatItemView.hbs

Testing strategy

1. Add Amazon SES secrets to your .env, https://gitlab.com/gl-gitter/secrets/-/blob/master/webapp/prod#L9-10
   • amazonses__accessKeyId
   • amazonses__secretAccessKey
2. Setup a room with some Matrix virtualUser messages
3. node .\scripts\utils\send-unread-notification-email.js --username MadLittleMods --room-uri MadLittleMods/postcss-css-variables --dummy=false

Todo

• Merge env!30 (merged)
• Install new version of @gitterhq/env