Implement read set for composite key get_state

Although reads and writes of composite keys are handled just like regular keys,
the `get_public_state_by_partial_composite_key` fetches a json blob with a set of kv pairs, which are unmarshalled and passed to the caller. As of #501 FPC does not keep track of this set in the rwset. Also the kv pairs cannot be simply put in the read set, because they are not the result of single reads.

Handling this properly requires to handle the [RangeQueryInfo](https://github.com/hyperledger/fabric-protos/blob/74ca5deb7ed6418f3dea4a47eda4e98eaa8182f7/ledger/rwset/kvrwset/kv_rwset.proto) protobuf, include it in the rwset protobuf, and finally check and replay it at endorse time.