Issue #3225961 by hanoii: Overridden API on settings doesn't expand config form
- From Mandrill Issue 3225961 https://www.drupal.org/project/mailchimp_transactional/issues/3225961
Closes #3225961
- Adds better admin settings form handling when API Key is overriden
- Shows full form if API key is overriden
- When the API key is being overridden, show a warning and no longer require API Key on admin form
- Only validate form api keys
- Readme updates with clarification on use