always set a valid default institute for each user, fixes #3978


git-svn-id: svn://develop.studip.de/studip/trunk@28962 c5b85792-5220-0410-ad23-ed5b6b8ad999
rename namespace API to RESTAPI, refs #3484

git-svn-id: svn://develop.studip.de/studip/trunk@28963 c5b85792-5220-0410-ad23-ed5b6b8ad999