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.
Merge branch 'master' into codeception-test-adjustments

Conflicts:
	.travis.yml
Fixed templates and fixtures paths for advanced application
Removed db module from basic app, renamed _helpers to _support and _logs to _output
Renamed guy classes to actors, fixed phpdoc and code style
Exposed basic app entry URL via codeception.yml, refactored configs of advanced app to read from config and define entry script in a single place
Attempt to fix travis
Merge branch 'master' into codeception-test-adjustments
Added missing cd to travis
Fixed travis paths
Adjusted test configs structure
Fixed copyright year in batch files
Removed unneeded && from travis
Use separate webservers for basic and advanced apps in travis
Fixed tabs in yml
Split command for easier debug
Proper exit codes for codeception tests
Prefixed constants to avoid possible naming conflicts
Fixes #4640: Added `yii\widgets\ActiveForm::beginField()` and `endField()`
Multiple flash messages per type support