[TASK] add basic reload functionality

frontend/main.ts

@@ -16,6 +16,7 @@ document.addEventListener('DOMContentLoaded', function() {
   initBoatActions();
   selectBoatChange();
   addRelationMagic(<HTMLElement>document.querySelector('body'));
+  reloadPage();
 });
 
 function selectBoatChange() {
@@ -67,6 +68,22 @@ function selectBoatChange() {
   }
 }
 
+function reloadPage() {
+  let pageTitle = document.title;
+  let attentionMessage = 'Riemen- und Dollenbruch';
+
+  document.addEventListener('visibilitychange', function() {
+      let isPageActive = !document.hidden;
+
+      if(!isPageActive){
+          document.title = attentionMessage;
+      }else {
+          document.title = pageTitle;
+          location.reload();
+      }
+  });
+}
+
 function setMaxAmountRowers(rowers: number){
 	  let curSelection = choiceObjects['newrower'].getValue(true);
 	  	let amount_to_delete = (<any>curSelection).length - rowers;