Initial TbCarousel implementation

So we have had TbHtml::carousel() for some time, but to make the carousel start automatically all the scripts have to be registered manually. This widget is basically a wrapper around TbHtml::carousel() which takes care of registering event handlers and the proper Javascript to start the carousel automatically.

Note that it doesn't register bootstrap.js even though it's required. I prefer to register the individual scripts myself (bootstrap-carousel.js and bootstrap-transition.js in this case), but maybe there should be a disableScripts option that default to false? What do you think @Crisu83?