message: Allow `unsafeSplit` when doing `/tx/send`
  Summary:
  Reviewers: mark, bigly, tyler, dawid
  Subscribers: tyler
diff: @@ -357,7 +357,7 @@ Wallet.prototype.consolidateUnspents = function consolidateUnspents(params, call
  const transactionParams = _.extend({}, params, { txPrebuild: response, keychain: keychain });
  const signedTransaction = yield this.signTransaction(transactionParams);
  - const selectParams = _.pick(params, ['comment', 'otp']);
  + const selectParams = _.pick(params, ['comment', 'otp', 'unsafeSplit']);
  const finalTxParams = _.extend({}, signedTransaction, selectParams);
  this.bitgo._reqId = reqId;
  @@ -402,7 +402,7 @@ Wallet.prototype.fanoutUnspents = function fanoutUnspents(params, callback) {
  const transactionParams = _.extend({}, params, { txPrebuild: response, keychain: keychain, prv: params.xprv });
  const signedTransaction = yield this.signTransaction(transactionParams);
  - const selectParams = _.pick(params, ['comment', 'otp']);
  + const selectParams = _.pick(params, ['comment', 'otp', 'unsafeSplit']);
  const finalTxParams = _.extend({}, signedTransaction, selectParams);
  this.bitgo._reqId = reqId;
  return this.bitgo.post(this.baseCoin.url('/wallet/' + this._wallet.id + '/tx/send'))
  @@ -479,7 +479,7 @@ Wallet.prototype.sweep = function sweep(params, callback) {
  const transactionParams = _.extend({}, params, { txPrebuild: response, keychain: keychain, prv: params.xprv });
  const signedTransaction = yield this.signTransaction(transactionParams);
  - const selectParams = _.pick(params, ['otp']);
  + const selectParams = _.pick(params, ['otp', 'unsafeSplit']);
  const finalTxParams = _.extend({}, signedTransaction, selectParams);
  this.bitgo._reqId = reqId;
  return this.bitgo.post(this.baseCoin.url('/wallet/' + this._wallet.id + '/tx/send'))
  @@ -1142,7 +1142,7 @@ Wallet.prototype.prebuildAndSignTransaction = function(params, callback) {
  * @param callback
  */
  Wallet.prototype.submitTransaction = function(params, callback) {
  - common.validateParams(params, [], ['otp', 'txHex'], callback);
  + common.validateParams(params, [], ['otp', 'txHex', 'unsafeSplit'], callback);
  return this.bitgo.post(this.baseCoin.url('/wallet/' + this.id() + '/tx/send'))
  .send(params)
  .result()
  @@ -1250,7 +1250,7 @@ Wallet.prototype.sendMany = function(params, callback) {
  'message', 'minValue', 'maxValue', 'sequenceId',
  'lastLedgerSequence', 'ledgerSequenceDelta', 'gasPrice',
  'noSplitChange', 'unspents', 'comment', 'otp', 'changeAddress',
  - 'instant', 'memo'
  + 'instant', 'memo', 'unsafeSplit'
  ]);
  const finalTxParams = _.extend({}, halfSignedTransaction, selectParams);
  this.bitgo._reqId = reqId;
  