Merge
new update script
script 404 fixes
fix for bug introduced with c9953d259af573c732e3fb520bc74db2587aa42f
lecturer course overview: new-style buttons

fixes #17
questions without lecturers should appear first

fixes #22
some translation issues

fixes #2
getting rid of some tabs
some link fixes

fixes #26
more stable questionnaire ordering

fixes #14
remove obsolete questionnaires in assignment forms

fixes #24
show lecturer menu if lecturer is marked as lecturer or a proxy for a lecturer

fixes #20
template validation for email templates

cf. #15