Add the ability to manage CSP extensions for a specific content item from the main interface.

[GeekInTheNorth]

Currently the CMS Editor can extend the CSP for a singular content item directly against that particular page, however the administrator will not be able to view that in the security interface or understand how many pages have been extended.

Add the ability to view the additional sources on the CSP sources tab. This control can be hidden if none exist.
Add a scheduled job to find and store this information for use by the module.
Add a post publish event to retrieve and store this information for use by the module.
Add the ability to include the selected sources as read-only alongside other sources.
Add the ability to update the preview screen.