Summary: This reduces page jitter (moving around) after page load.

This feature depends on a cookie that is synchronized with LocalStorage
    This cookie can be set either by JS when LS is changed
        or from the server side, by route.php

The downside is that when user changes settings, page must be reloaded.
This should be fixed in the future. #todo

This is to assist the modular UI, which consists of three layers (specified as class):
beginner
advanced
admin

(Not all elements have a class, and all elements are visible by default.

Each of these groups may be hidden depending on user settings. In order to prevent page elements from jumping around, we can pre-set their visibility with an injected style.

This setting enables such injection. Based on the following three cookies, the respective element groups will be hidden when the cookie is set to 0.

beginner
show_advanced
show_admin

Styles like this will be inserted into the page when cookie is set to 0:

.beginner { display: none; }
.advanced { display: none; }
.admin { display: none; }

It helps remediate UI jumping around after page load.
