Cleaner approach to things related to stores and queries

* got rid of the Free[Command]
* RDFStore is now a typeclass
* it is made of 3 three independent ones: GraphStore, SparqlEngine, Transactor
* there is an additional Lifecycle typeclass for start/stop operations
  * it comes with a default instance doing nothing
* syntax enhancement are made available from within the typeclass themselves
That's an old discussion.

In theory, this would be a good idea. In practice, Monad is not enough. You'd need something that handle failures too. And a comonad too. I am not sure this is worth it.

Future is a good approximation here.