Clear, review and improve presentation of contributed extension profiles

[anjackson]

• [x] Make basic stats visible when profile selected. in top list (?)
• [x] Add clearer context/support info for the selected registry.
• [x] Need to declare which container formats have been opened? Need to add a caveat about the limitations of not opening up containers?
• [x] Make 'uniqueness' clear, document canonicalisation process.