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)
[Here](http://symfony.com/doc/current/book/service_container.html#using-the-expression-language) is an usage example with ```parameter()``` function. It comes from Symfony official documentation but I haven't tested it.

I've only tried the ```constatnt()``` function, and it works.