Make window titles translatable

config/Windows/editinvoiceitem.xml

     <program>
         <![CDATA[
             window = this;
-            this.windowTitle = 'Typica - Item Detail';
+            this.windowTitle = TTR("invoiceitemdetail", "Typica - Item Detail");
             var nameField = findChildObject(this, 'name');
             var referenceField = findChildObject(this, 'reference');
             var costField = findChildObject(this, 'cost');

config/Windows/purchase.xml

 				}
 				return w;
 			};
-            this.windowTitle = 'Typica - Coffee Purchase';
+            this.windowTitle = TTR("purchase", "Typica - Coffee Purchase");
             var form = findChildObject(this, 'form');
             form.setMaximumElementHeight(320);
             var appendForm = function() {