optimize images from [27473] and [27474] for size, re #3419

git-svn-id: svn://develop.studip.de/studip/trunk@27483 c5b85792-5220-0410-ad23-ed5b6b8ad999
fix double render bug re #3406

git-svn-id: svn://develop.studip.de/studip/trunk@27484 c5b85792-5220-0410-ad23-ed5b6b8ad999