Fixes to use Bootstrap 3.0.0-RC1, with the KnpMenuBundle rendering working

Hello,

This PR includes all the small fixes needed to use the new Bootstrap 3.0.0-RC1 provided by [twitter/bootstrap](https://packagist.org/packages/twitter/bootstrap) package. Additionally, it also includes the fixes to the KnpMenuBundle rendering so it uses the new HTML.

This might break the rendering of other custom components, like forms and pagination, which I will be working on next.