More optimisation and cleanup (#420)

templates/partials/dark_theme.html

@@ -0,0 +1,7 @@
+{% load static %}
+<script>
+if({{ request.user.dark_theme|lower|default:'false' }} || window.matchMedia('(prefers-color-scheme: dark)').matches) {
+    $('<link>').prependTo('head').attr({type : 'text/css', rel : 'stylesheet'}).attr('href', '{% static "css/dark_screen.css" %}');
+    document.body.setAttribute('data-theme', 'dark');
+}
+</script>