change copayerId to use sjcl sha256 over xpub

lib/server.js

@@ -222,7 +222,7 @@ CopayServer.prototype.joinWallet = function(opts, cb) {
       self.storage.fetchCopayerLookup(copayer.id, function(err, res) {
         if (err) return cb(err);
         if (res)
-          return cb(new ClientError('CREGISTED', 'Copayer ID already registered on server'));
+          return cb(new ClientError('CREGISTERED', 'Copayer ID already registered on server'));
 
         wallet.addCopayer(copayer);
         self.storage.storeWalletAndUpdateCopayersLookup(wallet, function(err) {

lib/walletutils.js

@@ -61,8 +61,8 @@ WalletUtils.getProposalHash = function(toAddress, amount, message) {
 };
 
 WalletUtils.xPubToCopayerId = function(xpub) {
-  //return (new Bitcore.HDPublicKey(xpub)).derive(HDPath.IdBranch).publicKey.toString();
+  var hash = sjcl.hash.sha256.hash(xpub);
-  return crypto.Hash.sha256(new Buffer(xpub)).toString('hex');
+  return sjcl.codec.hex.fromBits(hash);
 };
 
 WalletUtils.toSecret = function(walletId, walletPrivKey, network) {