Eng 6095 index with address

Don't merge, only for review.

Pass eecheck on local machine, but haven't check the result of Junit test.

I worry about how to deconstruct Key and Data: is the default deconstructor enough?

After refining the code, the next step is to append address to KeyType other than IntsKey.
This class is where I would define accessor functions like getKey and getValue to hide kv and its actual API in most cases. (And I think that the actual API to kv should be the std::pair API using first, second, etc.).