Added the batterytool to the website.

wwwroot/includes/apps.html

@@ -1,6 +1,7 @@
 <h1>Douwco Apps</h1>
 <div class="content-box">
-    <p>
-        Under construction...
-    </p>
+    <a href="/batterij-simulator">
+        <img class="icon small" src="/img/icons/projects_icon.png" alt="Icon">
+        <p>Battery <span>Simulator</span></p>
+    </a>
 </div>