now constructing XRP txs without the help of ripple-lib
now constructing XRP txs without the help of ripple-lib

Reviewers: alex, benchan

Reviewed By: benchan

Subscribers: ben

Differential Revision: https://phabricator.bitgo.com/D5313

BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS