#12 Consistency check for review due date wanted

[Karsten Gross]

A warning should be shown if the due date for a review cycle is in the past (or mark it red on entering) if review invitation is checked/executed (before or latest during <validate-input>). It should be the same day or in the future. Perhaps it's possible to enter a default value in the preferences that a due date should e.g. 7 days in the future and/or to introduce a new button beyond "Due Date"-field which is named "Default" and a tooltip shows the date (which corresponds to the date which is e.g. 7 days in the future).

This would help prioritizing the review tasks.