Conflicts:
	.travis.yml

- 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.

exclude parts that have different default values

fixes test break in HHVM due to export of a closure

Translated rest-rate-limiting.md and rest-error-handling into Russian [skip ci]

Fixes #4697: MSSQL query builder does not work for newer MSSQL versions when LIMIT is used without ORDER BY

Dynamic model typo fix

[ci skip] Fixing typo in guide-structure-modules

added source map generation so that styling can be debugged easily.

Fixes #4607: AR model will throw an exception if it does not have a primary key to avoid updating/deleting data massively

Updated yii.activeform.js to use the encode option introduced in #4122.
Updated ActiveForm with new option encodeErrorSummary

fixes #4690, close #4691

[ci skip]

Fix #4630: automatic generating of unique slug value to `yii\behaviors\Sluggable`