Include atomic
remove atomic_pointer.h references
BlockBasedTableConfig & PlainTableConfig enhancements

Summary:
BlockBasedTableConfig
- ported Checksum
- ported IndexType

PlainTableConfig
- added missing options
- added EncodingType

Test Plan:
make rocksdbjava
make jtest

Differential Revision: https://reviews.facebook.net/D26595
Integrated review comments by ankgup87

- Added tests
- Minor code-style changes