Renamed css to stylesheets and js to javascripts

Signed-off-by: Jim Martens <github@2martens.de>

_assets/javascripts/main.js

@@ -0,0 +1,33 @@
+//= require popper
+//= require bootstrap/util
+//= require bootstrap/collapse
+//= require bootstrap/tooltip
+
+"use strict";
+$(function() {
+    let mainMenu = $("#mainmenuNavbar");
+    mainMenu.on("show.bs.collapse", function () {
+        $("#submenuNavbar").addClass("invisible");
+    });
+    mainMenu.on("hidden.bs.collapse", function () {
+        $("#submenuNavbar").removeClass("invisible");
+    });
+
+    let backToTop = $("#back-to-top");
+    $(window).scroll(function () {
+        if ($(this).scrollTop() > 50) {
+            backToTop.fadeIn();
+        } else {
+            backToTop.fadeOut();
+        }
+    });
+    backToTop.click(function () {
+        backToTop.tooltip("hide");
+        $("body,html").animate({
+            scrollTop: 0
+        }, 800);
+        return false;
+    });
+
+    backToTop.tooltip();
+});