renaming rop chapters to start with rop-

(cherry picked from commit c878e990e4e966238055da2ca168a114fc9f3c05)

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/branches/STABLE-3.1@1555549 13f79535-47bb-0310-9956-ffa450edef68