Added implementations for the following:

    QueryExecutor.GetStateRangeScanIterator()
    QueryExecutor.GetStateMultipleKeys()
    TxSimulator.DeleteState()
    TxSimulator.SetStateMultipleKeys()

Unit testing was extended for the range query in couchdb.go

Additional unit testing for simulation functions will be added
following a refactoring of unit tests for goleveldb.

Change-Id: Id0907ace75767fe4b296f16c10d18693718d790f
Signed-off-by: Chris Elder <chris.elder@us.ibm.com>