Move integration tests to separate directory

Again, we do all of this to prepare for creating "real" test suites for
each type of tests.

tests/integration/TestCase.php

@@ -0,0 +1,31 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Tests\integration;
+
+use PHPUnit\Framework\TestCase as Test;
+
+abstract class TestCase extends Test
+{
+    use CreatesForum,
+        MakesApiRequests;
+
+    public function setUp()
+    {
+        $this->refreshApplication();
+        $this->init();
+    }
+
+    protected function init()
+    {
+        // .. allows implementation by children without the need to call the parent.
+    }
+}