Freeze tutorials: fixes and cleanup

- Move JS code samples to JS folder (future-proofing for other
  languages)
- Make "Freeze a Trust Line" tutorial interactive
- Add necessary functionality to interactive_tutorial helper JS
- Rework freeze a trust line tutorial/code sample to make an incoming
  line from another address and make looking up trust lines a
  full-fledged step

content/_code-samples/freeze/js/set-no-freeze.js

@@ -0,0 +1,39 @@
+// Dependencies for Node.js.
+// In browsers, use <script> tags as in the example demo.html.
+if (typeof module !== "undefined") {
+  // gotta use var here because const/let are block-scoped to the if statement.
+  var xrpl = require('xrpl')
+}
+
+async function main() {
+  // Connect -------------------------------------------------------------------
+  const client = new xrpl.Client('wss://s.altnet.rippletest.net:51233')
+  await client.connect()
+  console.log("Connected to Testnet")
+
+  // Get credentials from the Testnet Faucet ------------------------------------
+  console.log("Requesting an address from the Testnet faucet...")
+  const { wallet, balance } = await client.fundWallet()
+
+  // Submit an AccountSet transaction to enable No Freeze ----------------------
+  const accountSetTx = {
+    TransactionType: "AccountSet",
+    Account: wallet.address,
+    // Set the NoFreeze flag for this account
+    SetFlag: xrpl.AccountSetAsfFlags.asfNoFreeze
+  }
+
+  // Best practice for JS users - validate checks if a transaction is well-formed
+  xrpl.validate(accountSetTx)
+
+  console.log('Sign and submit the transaction:', accountSetTx)
+  await client.submitAndWait(accountSetTx, { wallet: wallet })
+
+  // Done submitting
+  console.log("Finished submitting. Now disconnecting.")
+  await client.disconnect()
+
+  // End main()
+}
+
+main().catch(console.error)