Make the settings button optional

The settings button will now be optional and will be enabled through the
config. If it is disabled, it will not be shown in the page.

By default, it is disabled, since adding it might ruin the look of the
startpage for a lot of users.

css/main.css

@@ -159,7 +159,8 @@ body {
   position: absolute;
   bottom: 25px;
   right: 25px;
-  transition: 2s ease-in; }
+  transition: 2s ease-in;
+  display: none; }
   #settings-cog:hover .cog {
     fill: white;
     stroke: white;