Provide a 'change' event to JX.Tokenizer

Summary: Provide an event like a 'change' event for <select />. The concrete
motivation for this is that we want to update the preview panel in Differential
and Maniphest when a user is executing an "Add Reviewers..." or "Add CCs..."
action and changes the users they're adding.

Test Plan: Installed a JX.Tokenizer listener for 'change', got events when I
altered the value of the tokenizer.

Reviewers: vrana, cpojer, aran, tomo, mroch

Reviewed By: cpojer

CC: aran, epriestley, cpojer

Differential Revision: https://secure.phabricator.com/D1280

src/lib/control/tokenizer/Tokenizer.js

@@ -35,6 +35,13 @@ JX.install('Tokenizer', {
     this._containerNode = containerNode;
   },
 
+  events : [
+    /**
+     * Emitted when the value of the tokenizer changes, similar to an 'onchange'
+     * from a <select />.
+     */
+    'change'],
+
   properties : {
     limit : null,
     nextInput : null
@@ -247,6 +254,8 @@ JX.install('Tokenizer', {
 
       root.insertBefore(token, focus);
 
+      this.invoke('change', this);
+
       return true;
     },
 
@@ -336,6 +345,9 @@ JX.install('Tokenizer', {
       delete this._tokenMap[index];
       this._redraw(true);
       this.focus();
+
+      this.invoke('change', this);
+
       return true;
     },