Register the custom security setting

package.json

@@ -7,6 +7,12 @@
   "main": "src/main.js",
   "author": "Thomas Rientjes",
   "preferences": [{
+    "name": "security_custom",
+    "title": "Using custom security preferences",
+    "hidden": true,
+    "type": "bool",
+    "value": false
+  }, {
     "name": "security_level",
     "title": "Tor browser security level",
     "hidden": true,