Pretty print request bodies

[visola]

User Story

As a user, I want to easily understand the payloads sent and received.

Acceptance Criteria

• There's an extra tab that the user can click to see the prettier version of the body
• The following formats should be pretty printed
  • JSON
  • HTML Forms
  • XML
  • HTML
  • Javascript
  • CSS
• All image formats should show as image

Depends on

#38