Codeception test adjustments for basic and advanced applications

- Moved everything test-related into `tests` directory. Codeception tests are in `codeception`.
- Removed database module since we're using fixtures and migrations.
- Moved console entry points and bootstrap into `tests/codeception/bin`.
- Adjusted travis build scripts.
- Adjusted documentation to be consistent and reflect changes made.

apps/advanced/tests/codeception/frontend/unit/TestCase.php

@@ -0,0 +1,8 @@
+<?php
+
+namespace codeception\frontend\unit;
+
+class TestCase extends \yii\codeception\TestCase
+{
+    public $appConfig = '@codeception/frontend/unit/_config.php';
+}