feat/change email

[th0rgall]

• docs: add comment about FullscreenControl container
• refactor: split off deleteContact for SendGrid
• feat: self-service email change & recovery
• fix: allow unconfigured Discourse variables
• fix: prevent multiple email change function calls in the modal
• fix: also sync the host field to new SendGrid conact on email change
• fix: use the user-configured communicationLanguage after login

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit ac685e7):

https://wtmg-dev--pr321-feat-change-email-b334ye7n.web.app

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