Added notifications.js

Creates overlay notifications from events and key strokes. improved
fading.
You don't need to update it here, but something that might make it easier for you to manage these items is to group everything in an object rather than as parallel arrays, ie:
```javascript
arrays.push({
    notice: notice,
    button: button,
    createTime: createTime
    ...
});
```

Then you can access it via `arrays[0].notice`.  This would also remove the need for your notifications/buttons/etc. arrays.