Develop: Add Actions panel below mail images

[mdconatser]

As a user, I want to be able to have a single UI panel containing the most relevant and actionable content below each mail image.

See mockups: https://xd.adobe.com/view/db7cd80e-542d-495d-8909-01d4b2607dbe-8e2f/screen/7e31c20e-0f52-470c-88d2-4912f3564f3d

Acceptance Criteria

• Any kind of UI panel that can support other elements being added to it in the future is appended to the email body after each image.
• Document any relevant content in the Programmer guide (draft thoughts of usage and importantly the "Why")
• Updates SRS and STP (and other docs if necessary)
• Add/Update relevant unit tests