Oauth school selector: Allow to chose 'no school' in school selector in order to allow to retreive old data

Admin interface: Set correct csrf tokens so groups and participations can now be deleted. Fixes #116

Admin interface: Make name search case insensitive in postgres, make oauth id search also look for oauth id without school id

UX tweaks: Template jwinf: Enhance notes for logincodes, admin interface: Show less id and more information about student / teacher / admin status

Oauth login: Throw error instead of silently ignoring school information not being configurerd on teacher login via PMS

Do not allow login with empty group code or empty login code even if an corresponding entry exists in the database

Enable configuration options to be passed through to certain (later possibly all) templates directly

Template jwinf: Optionally require field sex in profile, optionally allow 'no answer', 'diverse' or 'other', respectively, configurable via config file

Template jwinf: Require field grade, optionally allow grade to be 'not yet in school' with template argument

Make admin interface select participations by session id instead of session token. This allows to show participations of users, that have logged out.