- Reduce margin between checkboxes for matrix-receive node

- matrix-send-message node can now be used to reply in a thread (closes #104)
- matrix-receive node now returns msg.mentions for easier access to who was mentioned in message
- matrix-receive node now returns boolean msg.isThread based on whether the message is a thread reply or not

src/matrix-receive.js

@@ -1,3 +1,4 @@
+const {RelationType} = require("matrix-js-sdk");
 module.exports = function(RED) {
     function MatrixReceiveMessage(n) {
         RED.nodes.createNode(this, n);