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/basic/tests/codeception/functional/_bootstrap.php

@@ -0,0 +1,3 @@
+<?php
+
+new yii\web\Application(require(__DIR__ . '/_config.php'));