add ticket purchase page

Co-authored-by: Jan-Marlon Leibl <jleibl@proton.me>
Reviewed-on: http://git.simonis.lol/projects/abiball/pulls/13
Reviewed-by: jank1619 <jan@kjan.email>

src/Twig/Environment.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace App\Twig;
+
+use Twig\Extension\AbstractExtension;
+use Twig\TwigFunction;
+
+class Environment extends AbstractExtension
+{
+    public function getFunctions(): array
+    {
+        return [new TwigFunction('env', $this->getVar(...))];
+    }
+
+    public function getVar(string $name): string
+    {
+        return $_ENV[$name];
+    }
+}