Use of links between containers should be deprecated

As discussed in #463, docker networks seem mature enough to use, and links are officially not recommended any more.

We'd like to deprecate use of links; off the top of my head I believe we ought to do the following things:

• Obviously, mark the container addLink method as deprecated with a clear comment
• Links aren't currently documented very well, but update the docs with a clear enough description of the networking support, so that ad-hoc linking can be done easily by users
• Modify Webdriver VNC recorder sidecar container to remove use of links
• Modify Docker Compose support; can we remove use of the ambassador container now?

Comienza rastreando el soporte de Docker Compose y el uso que hace de su contenedor ambassador; después, inspecciona las pruebas relacionadas y el comportamiento actual de la red. Determina si se puede eliminar ambassador sin romper las pruebas basadas en Compose; se considera hecho cuando ya no se requieren links allí y el soporte existente de Compose sigue estando cubierto por pruebas satisfactorias.