frontend: Add perfectScrollbars to Settings/Organization overlay.

Use perfectScrollbar on settings sidebar, since the default scrollbar
makes settings menu break when not enough vertical space available.

Add perfectScrollbar to main settings section, and reset the scrollbar
position when switching between tabs.

Also delete the z-index on `.settings-list` since it makes the
perfectScrollbar covered.

Fixes #5216.

static/js/click_handlers.js

@@ -712,6 +712,8 @@ $(function () {
 
         $(".settings-section, .settings-wrapper").removeClass("show");
 
+        ui.update_scrollbar($("#settings_content"));
+
         if (is_org_section) {
             admin_sections.load_admin_section(section);
         } else {

static/js/settings.js

@@ -47,6 +47,9 @@ $("body").ready(function () {
 
 
 function _setup_page() {
+    ui.set_up_scrollbar($("#settings_page .sidebar.left"));
+    ui.set_up_scrollbar($("#settings_content"));
+
     // only run once -- if the map has not already been initialized.
     if (!map_initialized) {
         map = {

static/styles/components.css

@@ -321,6 +321,7 @@ a.no-underline {
     opacity: 0;
 
     transition: opacity 0.3s ease;
+    overflow: hidden;
 }
 
 .overlay.show {

static/styles/settings.css

@@ -852,7 +852,6 @@ input[type=checkbox].inline-block {
 
 #settings_page .sidebar .settings-list {
     position: relative;
-    z-index: 3;
 }
 
 #settings_page .content-wrapper {