- 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.

`yii\web\Request::cookieValidationKey` is now automatically generated by the installation script for the basic and advanced application templates

Fixes #2341, fixes #2317: moved codeception dependecies to "suggest" section, fixed codeception version on stable branch

This reverts commit 7145b9e9.

fixes #1913

no need to download codeception via composer when phar is used.
fixes #1913

fixes #1736

follow up to PR #1393