Catch and log handler exceptions in events.trigger

rather than throwing handler errors in the call to `.trigger()`

Extensions can register buggy event handlers.
These should not be able to cause failures in the event-triggering code paths.

This should fix several avenues where extensions (or other bugs) could prevent a notebook from loading.

notebook/static/base/js/events.js

@@ -22,5 +22,16 @@ define(['base/js/namespace'], function(Jupyter) {
     Jupyter.Events = window._Events;
     Jupyter.events = window._events;
     
-    return $([window._events]);
+    var events = $([window._events]);
+
+    // catch and log errors in triggered events
+    events._original_trigger = events.trigger;
+    events.trigger = function (name, data) {
+        try {
+            this._original_trigger.apply(this, arguments);
+        } catch (e) {
+            console.error("Exception in event handler for " + name, e, arguments);
+        }
+    }
+    return events;
 });