Merge pull request #1006 from tushargosavi/hds

Initial changes for WAL.
Change key type to Slice for equals and hashCode.
Merge pull request #1007 from tweise/hds

Change key type to Slice for equals and hashCode.
Maintain WAL metadata in operator state.
Use window-ids as log sequence numbers.
Merge branch 'hds' of github.com:DataTorrent/Malhar into hds

Conflicts:
	contrib/src/main/java/com/datatorrent/contrib/hds/HDSBucketManager.java
	contrib/src/test/java/com/datatorrent/contrib/hds/WALTest.java