add index populate events

In my project we are using bulk indexing, and according to [doc](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/indices-update-settings.html#bulk) to increase performant for bulk indexing, we need to have ability call custom actions like: `refresh_interval` and `_optimize?max_num_segments=5`

To achieve that we've added `PRE_POPULATE`, `POST_POPULATE`, `INDEX_RESET` events.