It's a common situation to remove an event listener inside its definition. Like this:
```javascript
viewer.on('load', function foo() {
	//code
	viewer.off('load', foo);
});
```

In this case `off` function removes the item from `externalEventListeners` array, while looping through this array may be not finished in `fireEvent` function. A reverse iteration fixes it.
Since we'd like to fire listeners in the order they were added, we need to use `externalEventListeners[type].length - i` index.

Fix removing event listeners / Fix 'setTimeout'

setTimeout(f(x), ms) executes function immediately and acts as if there is no setTimeout at all.

This reverts commit 8f436dbf48.

Add draggable option

Provide fallback cursor for IE / Edge