Allow to not generate extra use

For case when we not generate annotation (by default at doctrine orm:generate-entities) allow to not generate extra use for it - 
```php
use Doctrine\ORM\Mapping as ORM;
```
For example if generate entities for my project that use only dbal in pord but use orm for generate entities in dev mode.
Merge pull request #891 from spolischook/patch-2

Allow to not generate extra use