Refactor german (de) Zend_Validate.php

- Corrected placeholder token '%' for some translations
- Add new class names
- Replace '' with ""
Remove dublicated "eingegeben"
Fix typos
Fix typos
Replace "Eingabewert" with "Eingabe"
Replace "String" with "Zeichenkette"
Replace "String" with "Zeichenkette"
Replace "Integer" with "Ganzzahl"
Replace "Float" with "Gleitkommazahl"
Fix typo (wärend - während)
Merge branch 'feature/#6481-zend-validate-german-overhaul' into develop

Close #6481