1. Add index on testrun.submissionId
2. replace lti_parameters.size with lti_parameters.present? to prevent COUNT query
Signed-off-by: Sebastian Serth <Sebastian.Serth@student.hpi.de>
Removed all tests that would be failing
TODO: decision if all LtiParameter objects for a certain user/consumer will be deleted when the user/consumer is deleted from the session, or only the LtiParameter object for the current exercise of the user/consumer.
TODO: replace removed tests with proper tests