Switch custom Guzzle integration for Laravel's HTTP facade

Commit also adds config options to the example file.

.env.example

@@ -13,6 +13,11 @@ DB_DATABASE=laravel
 DB_USERNAME=root
 DB_PASSWORD=
 
+RECAPTCHA_SITE_KEY=
+RECAPTCHA_PRIVATE_KEY=
+RECAPTCHA_VERIFY_URL="https://www.google.com/recaptcha/api/siteverify"
+# WARNING: Your contact form will be useless if you change this value. Only change this URL if Google updates it.
+
 BROADCAST_DRIVER=log
 CACHE_DRIVER=file
 QUEUE_CONNECTION=sync