Allow to ask students for their matrikelnumber

This feature was added to be able to get a matrikelnumber if it is not accessible using the authentication filter (e.g. LDAP).

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Disable autocompletion for dynamic task answer fields

Signed-off-by: Sven Strickroth <email@cs-ware.de>