by adaping min/may yaw and max horizontal fov, this no background (empty space) shown

This reverts commit 2491c2b4dc.

Avoid loading invisible files for partial panos of any image type.

It never stops calling `animateMove`, if `pitch`, `yaw`, or `hfov` has not been changed.
Since we may have callback function, `animateMove` has to be called anyway, even if we don't actually need to animate movement. That's why equality of start and end positions is checked here, but not in `setPitch`, `setYaw`, and `setHfov`.

If `config.yaw` is close to -180 or 180, `yaw` might be out of bounds.

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.