also enhance test README

fixes #1311

Fixes #4938: When `yii\db\ActiveQuery` is used to build sub-queries, its WHERE clause is not correctly generated

- do not allow boolean values for integer columns
- use native boolean type with boolean values
- removed workaround that turned out to be wrong when schema and values
  are used correctly. Workaround resulted from wrong usage of boolean
  values before.

fixes #4672

Used a single database and a single CLI entry point for all test types. Added faker to basic app dev requirements.

- 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.

You can now customize test config without having uncommitted changes in
git.

issue #4687

also fixed an issue with default value loading of bool columns.

fixes #3489, fixes #4085, fixes #3920
related to #4672

close #4655