rpc: add method to get address deltas from a block

[kleetus]

based on current discussions, is this ready for review and test?

[braydonf]

Yes

[braydonf]

After discussion, I think we should take a look at these options before merging:

• Adding prevTxId and outputIndex to the addressindex value, so that it's possible to determine which utxo is being spent in the getaddressdeltas result, similar to the responses from getaddressmempool.
• LevelDB snapshots for the getaddressutxos command, to be able to query based on the last 6 block heights, to keep consistency across multiple requests for utxos at the same block height.
• Returning block height and hash in the response from getaddressutxos (and other methods) to determine of the results match the current expected height and hash.