Bundle and Component for dynamic configuration

Initial PR for discussing the component/bundle for dynamic configuration.

At the present state, a simple Entity holds a `Configuration`, which is a simple *key/value* store. The configuration Entity looks like this:

```php
protected $namespace = "";
protected $parameter;
protected $value;
```

A default adapter for using such an entity with doctrine `ORM` or `ODM` is proposed.
A second adapter to work with in memory/NOSQL key-value engines (such as `Redis`) is under way and needs to be discussed (Like injecting a specific `Redis` service or a more generic cache, like the [LiipDoctrineCacheBundle](https://github.com/liip/LiipDoctrineCacheBundle)

Some things need to be polished (like role intrefaces)
If we use current implementation, we should add here the `symfony/expression-language' dependency. We should add it in the `elcodi/elcodi` main composer as well.