Refactor Send XRP: reliable sub, folders by language

- Use reliable transaction submission methods where available
- Update text to describe the functions (esp. xrpl.js 2.0 stuff)
- Move Send XRP code samples to subfolders by language for consistency
  with other tutorials

content/_code-samples/get-started/js/base.js

@@ -1,3 +1,6 @@
+// In browsers, use a <script> tag. In Node.js, uncomment the following line:
+// const xrpl = require('xrpl')
+
 // Wrap code in an async function so we can use await
 async function main() {
 
@@ -7,7 +10,7 @@ async function main() {
 
   // ... custom code goes here
 
-  // Disconnect when done so Node.js can end the process
+  // Disconnect when done (If you omit this, Node.js won't end the process)
   client.disconnect()
 }