SDL: Select audio device (#2403)

* Initial Commit

Added Device logic to Sinks
Started on UI for selecting devices

Removed redundant import

* Audio Core: Complete Device Switching

Complete the device switching implementation by allowing the output
device to be loaded, changed and saved through the configurations menu.

Worked with the Sink abstraction and tuned the "Device Selection"
configuration so that the Device List is automatically populated when
the Sink is changed.
This hopefully addresses the concerns and recommendations mentioned in
the comments of the PR.

* Clean original implementation.

* Refactor GetSinkDetails

src/core/settings.h

@@ -104,6 +104,7 @@ struct Values {
     // Audio
     std::string sink_id;
     bool enable_audio_stretching;
+    std::string audio_device_id;
 
     // Debugging
     bool use_gdbstub;