Introduce JS container

This PR is my first try in order to fix egeloen/IvoryGoogleMapBundle#31

The helpers have been refactored in order to introduce a JS container. This will help a lot when we needs to deal with the Google Map API in the client side. 

This PR is a BC break for anyone who extends or uses directly these classes... Anyway, it is adressed for 1.0 (next major release).