Filter parameters config with expressions

This pull is related to https://github.com/doctrine/mongodb-odm/issues/899
It allows set filter parameters in config file.
Parse value parameter by [ExpressionLanguage](http://symfony.com/doc/current/components/expression_language/syntax.html)
I looked a bit further, and the the DI-specific expression functions are only supported via [ContainerBuilder::resolveServices()](https://github.com/symfony/symfony/blob/9567b9aac9ae49692af3ea6e4f2847bc3e4c9b4e/src/Symfony/Component/DependencyInjection/ContainerBuilder.php#L988). That is because the component defines its own ExpressionLanguage class (akin to what Security component does for its own functions and context).

While the ExpressionLanguage component _does_ allow custom functions to be registered, my point was that neither the two Symfony versions nor what we have here would be extensible, because we're constructing specific ExpressionLanguage classes internally. With the SecurityBundle, the expression language does happen to get defined as a service, so it would be extended with some hacking against the internal API, but I don't see anything in the documentation to encourage users to do so.