add NotFoundView

src/main/java/edu/kit/typicalc/view/main/NotFoundView.java

@@ -0,0 +1,27 @@
+package edu.kit.typicalc.view.main;
+
+import com.vaadin.flow.component.html.Div;
+import com.vaadin.flow.component.html.Label;
+import com.vaadin.flow.router.*;
+
+import javax.servlet.http.HttpServletResponse;
+
+@ParentLayout(MainViewImpl.class)
+public class NotFoundView extends Div
+        implements HasErrorParameter<NotFoundException> {
+
+    private final Label error = new Label();
+
+    public NotFoundView() {
+        add(error); // todo make more beautiful
+    }
+
+    @Override
+    public int setErrorParameter(
+            BeforeEnterEvent event,
+            ErrorParameter<NotFoundException> parameter) {
+
+        error.setText("Cannot find URL: " + event.getLocation().getPath());
+        return HttpServletResponse.SC_NOT_FOUND;
+    }
+}