Add CMF bundles and minimal configuration for the CMF

In this branch, we start using Doctrine PHPCR-ODM and the CMF bundles. To set up the repository, you need to run the following commands (after running `composer install` and making sure you configured a good Doctrine DBAL connection):

    php app/console doctrine:database:create
    php app/console doctrine:phpcr:init:dbal
    php app/console doctrine:phpcr:repository:init