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/unit/models/UserTest.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace codeception\unit\models;
+
+use yii\codeception\TestCase;
+
+class UserTest extends TestCase
+{
+    protected function setUp()
+    {
+        parent::setUp();
+        // uncomment the following to load fixtures for user table
+        //$this->loadFixtures(['user']);
+    }
+
+    // TODO add test methods here
+}