Lazy update attributes callback

[marcosgz]

Add new update_lazy_attribute_callback callback type to models. This callback should be used to perform bulk update to the lazy_document_attribute defined in the index repository.

Also refactored all the callback structure in order to support multiple types of callbacks. Opened this interface for external applications add its own custom callback. It's part of upcoming features for async indexing with Sidekiq and Faktory.

The index_callbacks was renamed to index_callback and esse_index_repos renamed to esse_callbacks. They are deprecated and will be removed by the end of this year.