refactor: move static sites into static, Remove unused PageController and update main.js for page navigation

src/main/java/de/uni_passau/fim/PADAS/group3/DataDash/controler/PageController.java

@@ -1,12 +0,0 @@
-package de.uni_passau.fim.PADAS.group3.DataDash.controler;
-
-import org.springframework.stereotype.Controller;
-import org.springframework.web.bind.annotation.GetMapping;
-
-@Controller
-public class PageController {
-    @GetMapping("/add")
-    public String getAddPage() {
-        return "add";
-    }    
-}

src/main/resources/static/main.js

@@ -81,8 +81,7 @@ for (const downvoteButton of downvoteButtons) {
 
 // functions of the main page
 function navigateToAdd() {
-    //TODO: url to add page not yet implemented, add here
-    window.location.href = "/add";
+    window.location.href = "/add.html";
 }
 
 function filter(filterString) {