rpc: deprecate addresses and reqSigs from rpc outputs

1) add a new sane "address" field (for outputs that have an
   identifiable address, which doesn't include bare multisig)
2) with -deprecatedrpc: leave "reqSigs" and "addresses" intact
   (with all weird/wrong behavior they have now)
3) without -deprecatedrpc: drop "reqSigs" and "addresses" entirely,
   always.

test/functional/wallet_basic.py

@@ -600,7 +600,7 @@ class WalletTest(BitcoinTestFramework):
         destination = self.nodes[1].getnewaddress()
         txid = self.nodes[0].sendtoaddress(destination, 0.123)
         tx = self.nodes[0].decoderawtransaction(self.nodes[0].gettransaction(txid)['hex'])
-        output_addresses = [vout['scriptPubKey']['addresses'][0] for vout in tx["vout"]]
+        output_addresses = [vout['scriptPubKey']['address'] for vout in tx["vout"]]
         assert len(output_addresses) > 1
         for address in output_addresses:
             ischange = self.nodes[0].getaddressinfo(address)['ischange']