Add form reset support

Author: Graham Butler

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@author.io/element-menu",
-  "version": "1.0.16",
+  "version": "1.0.17",
   "description": "author-menu custom element (web component).",
   "main": "dist/author-menu.min.js",
   "scripts": {

src/element.js

@@ -329,6 +329,12 @@ class AuthorMenuElement extends AuthorBaseElement(HTMLElement) {
 
     this.PRIVATE.sourceForm = sourceElement.form
 
+    if (this.PRIVATE.sourceForm !== null) {
+      this.UTIL.registerListeners(this.PRIVATE.sourceForm, {
+        reset: evt => this.deselectAll()
+      })
+    }
+
     this.UTIL.defineProperty('sourceElement', {
       readonly: true,
       default: sourceElement