Modified extension guidlines

Fixes #1654: Fixed the issue that a new message source object is generated for every new message being translated

GII generates rules for unique indexes

Number validator was missing

The signature for `yii\gridview\ActionColumn::urlCreator` is changed - the `$action` parameter is moved to the first

Fix wrong array index in unique indexes for MySql

Get DB unique indexes information

Proposal for #66: auth client implementation

Fixes #1610: `Html::activeCheckboxList()` and `Html::activeRadioList()` will submit an empty string if no checkbox/radio is selected

extended from codeception testcase, added docs

Gii should keep horizontal layout