refactor(build): modularize JS code

- replace gulp with rollup
- remove JS output from repo

_javascript/modules/layouts/basic.js

@@ -0,0 +1,7 @@
+import { back2top } from '../components/back-to-top';
+import { loadTooptip } from '../components/tooltip-loader';
+
+export function basic() {
+  back2top();
+  loadTooptip();
+}

_javascript/modules/layouts/sidebar.js

@@ -0,0 +1,7 @@
+import { modeWatcher } from '../components/mode-watcher';
+import { sidebarExpand } from '../components/sidebar';
+
+export function initSidebar() {
+  modeWatcher();
+  sidebarExpand();
+}

_javascript/modules/layouts/topbar.js

@@ -0,0 +1,9 @@
+import { convertTitle } from '../components/convert-title';
+import { displaySearch } from '../components/search-display';
+import { switchTopbar } from '../components/topbar-switcher';
+
+export function initTopbar() {
+  convertTitle();
+  displaySearch();
+  switchTopbar();
+}