implemented editing of document in GUI + respective handlers in backend

translations/src/main/resources/de.json

@@ -16,12 +16,15 @@
     "date": "Datum",
     "delete": "löschen",
     "email": "E-Mail",
+    "footer": "Fuß-Text",
     "gross_sum": "Brutto-Summe",
+    "head": "Kopf-Text",
     "list": "Dokumente",
     "list_of": "Dokumente von {0}",
     "net_price": "Nettopreis",
     "number": "Nummer",
     "pos": "Pos",
+    "positions": "Positionen",
     "select_company" : "Wählen Sie eine ihrer Firmen:",
     "select_customer": "Kunde auswählen",
     "sender": "Absender",