Use global configuration object

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Allow to configure mail server settings within context

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Allow to configure mail domain within context

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Allow to hide matrikelno from tutors

Signed-off-by: Sven Strickroth <email@cs-ware.de>
Allow to specify template in context settings

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