Move all classes located in the Adapter namespace to the Driver namespace

After discuss with @tmartin, we have decided to move all classes located in the `Adapter` namespace to the `Driver` namespace. `Adapter` means nothing in the DBAL perimiter (it is only a design pattern we have applied). So, we have decided to totally remove his usage. 

Moving all classes to the Driver namespace makes sense as one of the driver responsability is to instanciate a **native** connection. `Native` will be used to prefix the current `Adapter` `ConnectionInterface` & `StatementInterface` in order to make a difference between the DBAL ones.

To organize the classes, we will put all native connections in the `Fridge\DBAL\Driver\Connection` namespace & all native statements in the `Fridge\DBAL\Driver\Statement` namespace.