use jquery ui resizable() only if browser does not support native resizing, re #3479

git-svn-id: svn://develop.studip.de/studip/trunk@26528 c5b85792-5220-0410-ad23-ed5b6b8ad999
enlarge wiki editor, fixes #3479

git-svn-id: svn://develop.studip.de/studip/trunk@26529 c5b85792-5220-0410-ad23-ed5b6b8ad999