Also extended existing frontend tests for feedback creation.
In order to fix routing, partially refactored Subscription Vuex module #145

For now, every occurence of "student/s" that is visible to the user has been renamed to "participant". We should however think about how we adress the naming in the future.

Also, the student is not greeted with the anonimised name anymore

fixes #131

Also, there is no annoying reload upon logout anymore

also removed one passible cause for memory leak. Feedback was unnecesarily stored in the store under state.feedback

Solution is no longer displayed on student page because it may contain grading information which has been changed during the grading process and would thus confuse the student

Use postgres:9.6 is ci

The student page will no longer crash should there be no feedback objects for submissions and display a message to the user explaining that the submission hasn't been corrected due to the exam beeing pass only.