Summary:
This PR also includes some cleanup, bugfixes and refactoring of the Java API. However these are really pre-cursors on the road to CompactionFilterFactory support.
Closes https://github.com/facebook/rocksdb/pull/1241

Differential Revision: D6012778

Pulled By: sagar0

fbshipit-source-id: 0774465940ee99001a78906e4fed4ef57068ad5c