configuration fixes

* moved CONFIG_MIDI and CONFIG_MIDI_IN to own blocks when constructing
  comboboxes in deviceconfig
* use Models::AddEntry in deviceconfig
* sub-handling of CONFIG_HEX16 and CONFIG_HEX20 in CONFIG_SELECTION
  block when constructing, and use corresponding config_setter
* make sure SCSI controller- and ISAMEM-deviceconfig calls up
  deviceconfig with an instance number
* midi input and midi output was mixed when constructing soundsettings
  when loading prev. settings

src/qt/qt_deviceconfig.hpp

@@ -19,7 +19,7 @@ public:
     explicit DeviceConfig(QWidget *parent = nullptr);
     ~DeviceConfig();
 
-    static void ConfigureDevice(const _device_* device);
+    static void ConfigureDevice(const _device_* device, int instance = 0);
     static QString DeviceName(const _device_* device, const char* internalName, int bus);
 private:
     Ui::DeviceConfig *ui;