- 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.

[ci skip]

Fixes #4597: `yii\composer\Installer::setPermission()` supports setting permission for both directories and files now (qiangxue)

Added support for arbitrary operators to Query::filterWhere, added support for arbitrary operators to Sphinx extension

- Removed `FileLoader` and used `\Twig_Loader_Filesystem` instead.
- Added support of Yii's aliases.
- Added `set()` that allows setting object properties.

Improved checks where substr_compare is used, replaced more substr + comapre cases with substr_compare