Debug mode and error handling - the symfony way.

This pull request introduces environments (dev and prod) and debug mode via environment variables.
You can now put your site in debug mode using this in your virtualhosts file:

    SetEnv FORK_DEBUG 1
    SetEnv FORK_ENVIRONMENT dev

This change was needed to set debug mode and environment early enough to initialize the bundles in the right mode.

This PR also introduces the SymfonyWebProfiler toolbar when your in the dev environment and you are in debug mode.

When in dev mode, errors are displayed with the Debug component instead off the Spoon version.