Be more specific about how to unlock oral exams

Currently the message to unlock oral exams is:
You have to pay a deposit in order to see oral exams. After submitting a report of your own oral exam you can get your deposit back.
which leads to many emails along the lines of "how do I pay the deposit?".

Proposed fix: Have an env variable that describes for every association how to pay the deposed (e.g. come by oVIS during office hours)