Faker controller improved

Improved faker extension. Related with this issue - https://github.com/yiisoft/yii2/issues/2291
I removed `realpath` for the following reasons:

- [here](https://github.com/Ragazzo/yii2/compare/faker_controller_improved?expand=1#diff-67e555402f0005d358d5a6b65c0d6e58L236) because file that should be written is not exists yet;
- [here](https://github.com/Ragazzo/yii2/compare/faker_controller_improved?expand=1#diff-67e555402f0005d358d5a6b65c0d6e58R361) because directory to which files will be written can be not existing, and it is also in confirmation message;