SignerListSet txn and InnerObjectFormats (RIPD-182):

Add support for the SignerListSet transaction as a step toward
multi-sign support.

As part of the SignerListSet implementation, add InnerObjectFormat
templates (similar to TxFormats and LedgerFormats) and enforce them
in STObject, STArray, and STParsedJSON.

src/ripple/app/main/Main.cpp

@@ -137,7 +137,9 @@ void printHelp (const po::options_description& desc)
            "     ripple_path_find <json> [<ledger>]\n"
            "     version\n"
            "     server_info\n"
+           "     sign\n"
            "     stop\n"
+           "     submit\n"
            "     tx <id>\n"
            "     unl_add <domain>|<public> [<comment>]\n"
            "     unl_delete <domain>|<public_key>\n"