EZP-23347 - As a developer I would like to handle disabled/enabled state of a button

https://jira.ez.no/browse/EZP-23347

**THINGS DONE:**
- [x] added disabled state event handler,
- [x] updated CSS,
- [x] updated HTML,
- [x] updated JS unit tests
nitpick: you don't really need to subscribe to the change event, this test could be written in the following way:
```js
view.render();
view.set('disabled', true);
Y.Assert.isTrue(view.get('container').one('.action-trigger').hasAttribute('disabled'));
```