Change behaviour of starting year field in registrations

Ghost User
2019-10-08T13:54:44+02:00

1. Start a new member registration
2. The field currently contains the next lecture year
3. People make mistakes and select that one instead of the current lecture year

#### New behaviour
Steps to validate that it works:

1. Start a new member registration
2. The field currently contains the next lecture year
3. People make mistakes and select that one instead of the current lecture year