preserving 'images' folder to prevent failing builds

(cherry picked from commit 1c6e586f8d64a05089eca573957fd9deec2da7fe)

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/branches/STABLE-3.1@1555728 13f79535-47bb-0310-9956-ffa450edef68