added faker fixture command

Done, this is for issue https://github.com/yiisoft/yii2/issues/1506
Things to discuss:

1. i think we need basic fixture command that will have ```actionUp```/```actionDown``` to apply fixtures to the table or reset table, very simple to implement. Also this will help ```faker\FixtureController``` to be more useful for users because of ```faker\FixtureController < console\FixtureController```

2. Do we need README.md in the extension repo?

3. Can create tests if needed.

@samdark @qiangxue maybe some other thoughts/suggestions? other developers? :)