Add helper script for updating local address file

Can be run after starting the devchain, so that all local truffle
scripts work with the new network ID.

scripts/helpers/update_local_networkid.js

@@ -0,0 +1,22 @@
+const fs = require('fs');
+const getNetworkId = require('./networkid.js');
+
+module.exports = async function(callback) {
+  const daoAddressPath = 'lib/addresses/dao.json';
+
+  // TODO maybe do the same for KreditsKit address file
+  try {
+    const networkId = await getNetworkId(web3);
+    const daoAddresses = JSON.parse(fs.readFileSync(daoAddressPath));
+    const oldNetworkId = Math.max(...Object.keys(daoAddresses).map(a => parseInt(a)));
+    const localDaoAddress = daoAddresses[oldNetworkId];
+    daoAddresses[networkId] = localDaoAddress;
+    delete daoAddresses[oldNetworkId];
+    fs.writeFileSync(daoAddressPath, JSON.stringify(daoAddresses, null, 2));
+    console.log('Updated local network ID for DAO address');
+  } catch(e) {
+    console.log(e);
+  }
+
+  callback();
+};