refine layout for addclip according to gui-feedback refs #4525


git-svn-id: svn://develop.studip.de/studip/trunk@31466 c5b85792-5220-0410-ad23-ed5b6b8ad999
refine startpage layout according to gui-feedback, make h1 only visible to screen-readers refs #4626


git-svn-id: svn://develop.studip.de/studip/trunk@31467 c5b85792-5220-0410-ad23-ed5b6b8ad999