Change behavior of the "unbekannt" checkbox

[silvermane]

In the player dialog box (Spieler und Trainer verwalten) wouldn't it perhaps be better to make the "unbekannt" checkbox checked by default and leave the date fields blank. Often when inputting a new player you don't have his birthday on hand and you must click "unbekannt" for the program to accept your input. If you enter something in the date field the "unbekannt" box should be cleared.

Also, if you press [Tab] in the "Vollständiger Name" field twice, the cursor goes to the year (third) field instead of the day (first) field.