XWiki Platform privilege escalation (PR) from account through AWM content fields

XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. Any registered user can use the content field of their user profile page to execute arbitrary scripts with programming rights, thus effectively performing rights escalation. This issue is present since version 4.3M2 when AppWithinMinutes Application added support for the Content field, allowing any wiki page (including the user profile page) to use its content as an AWM Content field, which has a custom displayer that executes the content with the rights of the `AppWithinMinutes.Content author, rather than the rights of the content author. The vulnerability has been fixed in XWiki 14.10.5 and 15.1RC1. The fix is in the content of the AppWithinMinutes.Content page that defines the custom displayer. By using the display` script service to render the content we make sure that the proper author is used for access rights checks.