Added methods for changing values after initialization

I have added a few utility methods for changing values after the initialization has finished:

* `setOnLabel` changes the "On" text with a custom one
* `setOffLabel` changes the "Off" text with a custom one
* `setOnClass` sets the "On" class (`info`, `success`, etc.)
* `setOffClass` sets the "Off" class (`info`, `success`, etc.)
* `setAnimated` changes the `data-animated` attribute, thus changing the animation behavior
* `setSizeClass` sets the size of the component

I need all of this stuff because I'm about to release an AngularJS directive based on this nice plugin :)