Removed redundant code.
delay validation of scenario to validate().
Fixes issue #592: I18N t() plural forms possibly broken
added subsection to docs index
model guide
added dabase basics docs
removed dao section from docs
Update model.md
activerecord draft
Update database-basics.md
better sentence for label example.
fixed code blocks in migration docs
Removed part about extending attributes which is not basic usage

Discussion is here:
https://github.com/yiisoft/yii2/commit/9bc5868dd1f1d843c133d73726fd3f01197a3d5d#commitcomment-3552713
Using template engines docs
more structure for doc index
added note about model validation
renamed "logging" to "log".
Refactored logging.
Fixed test breaks.