Allow services class declaration to be overridden

Now you can inject whatever Spec Writer/Generator you need

@see http://symfony.com/doc/current/cookbook/bundles/override.html#services-configuration

Generate workflow Specification from CodeBase

Add CLI command gmorel:state-engine:generate-workflow-specifications

Allow generating workflow specifications as simple html file
Aim is to ease workflow visualization
And to have a rendered workflow always ISO to the one written in the code base
And this generated automatically and regularly

The code base is always up to date and reflects the specs
No forgotten - No human error