changed bootstrap namespace to jui

- 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.

changed problem to problems to correct a minor typo.

Fixes #4659: adjusted nginx config in docs to serve 404 instead of "no input file specified" when accessing non-existing PHP file

Backslash after alias causes 'Invalid path alias' exception in `\yii\BaseYii::getAlias`

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.

Updated guide