SONATA-308 - Add "add to basket" to be handled in popin

I've added "add to basket" action in a Bootstrap modal. Looks like this:

![capture decran 2013-12-20 a 15 42 18](https://f.cloud.github.com/assets/103900/1790985/08c92562-6985-11e3-8f86-aef36aeccc95.png)

This PR requires the following PR to be merged before to enabled Bootstrap JS library in PageBundle and not only on AdminBundle: https://github.com/sonata-project/SonataPageBundle/pull/248