image thumbnails: made the progressive jpeg option more meaningful in the frontend (text)

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@2170 1f8fe7d8-47f0-464c-8d0a-336f4953ab05
object diff: show empty string instead of "unknown"

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@2171 1f8fe7d8-47f0-464c-8d0a-336f4953ab05
do not show "undefined" in case there are no relations

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@2172 1f8fe7d8-47f0-464c-8d0a-336f4953ab05