Refactor SubscriptionWorkPage/Subscription Vuex Module
Summary
The Subscription work page and the corresponding Vuex module are one the most important parts of the application but a frequent source of bugs, e.g. #144 (closed). The interface should be functionally the same.
Todos
- the Subscription module and the Workpage should only always be concerned with the current assignment -> No prefetching!
- the whole correction workflow should be thoroughly tested by e2e tests