1. Remove unnecessary samples.
2. Add configuration file location note for basic application.
3. Fix a couple of typos.

Corrections in docs and Model::loadMultiple fix

* Documentation corrections for data population and quoting names in SQL query

Discussion is here:
https://github.com/yiisoft/yii2/commit/9bc5868dd1f1d843c133d73726fd3f01197a3d5d#commitcomment-3552713