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/test_runner.py

@@ -286,6 +286,7 @@ BASE_SCRIPTS = [
     'feature_config_args.py',
     'feature_settings.py',
     'rpc_getdescriptorinfo.py',
+    'rpc_addresses_deprecation.py',
     'rpc_help.py',
     'feature_help.py',
     'feature_shutdown.py',