Events dependency

Both the Slider and Rangeslider widgets depend on the `events` module to function correctly. The integration tests currently pass because [they explicitly load the `init` module](https://github.com/jquery/jquery-mobile/blob/8197bb0f78c89224d86975ba13cf1b1f5de028d9/tests/integration/forms/index.html#L30), which has a dependency on the `events` module.

This implicit dependency causes the following problems:

- The modules in question cannot be cleanly loaded from AMD projects
- It is possble to create broken [custom builds](http://jquerymobile.com/download-builder/) of jQuery Mobile (for instance, by selecting only the "Slider" widget)