[enhance] Driver/Interface selection/querying

This should be a quick fix:

Adding
```C++
  bool selectAudioInterface : 1;
  bool isPlugin : 1;
  bool dummyFlags : 30;
```
to DevicePrivate, would allow the application to know easily if the driver is capable of performing this task. To actually do it, it would be simple to use a virtual function.

As for Driver selection itself, this can be implemented in a single place. However, naturally it doesn't make sense to allow a stand-alone application to select a plugin driver, or for a plugin  to select any driver at all. So perhaps if a Native driver is selected, plugins should not be selectable, and so on.

I will provide a way to query this information.