Add i18n translation for Author labels (#311)

Closes #310

Author: beckermarc

app/_i18n/i18n.properties

@@ -25,6 +25,10 @@ Author = Author
 AuthorID = Author ID
 Name = Name
 AuthorName = Author's Name
+DateOfBirth = Date of Birth
+DateOfDeath = Date of Death
+PlaceOfBirth = Place of Birth
+PlaceOfDeath = Place of Death
 
 Order = Order
 Orders = Orders

app/_i18n/i18n_de.properties

@@ -25,6 +25,10 @@ Author = Autor
 AuthorID = ID des Autors
 Name = Name
 AuthorName = Name des Autors
+DateOfBirth = Geburtsdatum
+DateOfDeath = Sterbedatum
+PlaceOfBirth = Geburtsort
+PlaceOfDeath = Sterbeort
 
 Order = Bestellung
 Orders = Bestellungen