[Transformer] Add index / type info to TransformEvent

[dkarlovi]

If you have the same entity bound to couple different indices, it makes sense for the transformation to be index-specific (for example, having index_en and index_de, loading proper locale in the transform event).

Would go a long way to allow multi-language indices integrated with Doctrine+Gedmo which is tracked in #227.

[damijank]

Hi all! Is there any activity to be expected in this thread? index_name could do just fine if it were present in the TransformEvent's attributes...

[userz58]

Please, add property Index to FOS\ElasticaBundle\Event\PreTransformEvent FOS\ElasticaBundle\Event\PostTransformEvent

I can't catch the transformer for the desired index.