The database publisher

This is an initial idea of our DatabasePublisher (the class who will receive the benchmarks and store to database).

I commented the interface because of polyfractal/athletic#29

By the way, I didn't find a way to override Athletic default dependency container yet, please give me some light :smiley:

ping 
@Ocramius
@malukenho
@danizord
@gabrielsch  missing dockblock on `__construct()` method too.