https://jira.hyperledger.org/browse/FAB-602



The refactoring allows sharing of transaction execution and validation code across goleveldb and couchdb.
This refactoring also allows plugging-in different schemes for various aspects of transaction execution
such as maintianing isolation during simulation, validation and commit.

Change-Id: I0d3fb1cdff99c3f6f991e7b7469920173f194a87
Signed-off-by: manish <manish.sethi@gmail.com>

https://jira.hyperledger.org/browse/FAB-601


The height based versioning scheme assigns a version to the key equal to the  height of the transaction that committed it last.
The benefits include -
1) We do not need to maintain delete markers for the deleted keys
2) Makes recovery of state db easier, particularly for couchdb
3) Enables efficient validation - (in future - does not require validating against latest state has potential for in-memory validation)
4) Has potential for providing snapshot isolation across sharded data nodes in the future

Change-Id: I5a079c9be5966c349b7bb6c8df6e1a45d9889f1f
Signed-off-by: manish <manish.sethi@gmail.com>