if user is logged in, use that user as default rower

frontend/main.ts

@@ -5,6 +5,7 @@ export interface choiceMap {
   [details: string]: Choices;
 }
 
+declare var loggedin_user_id: string;
 let choiceObjects: choiceMap = {};
 let boat_in_ottensheim = true;
 let boat_reserved_today= true;
@@ -176,7 +177,9 @@ function selectBoatChange() {
               /** custom code for Etsch */
               choiceObjects["newrower"].setChoiceByValue("81");
           }
-        }
+        }else if (typeof loggedin_user_id !== 'undefined'){
+              choiceObjects["newrower"].setChoiceByValue(loggedin_user_id);
+	}
 
         const inputElement = document.getElementById(
           "departure",