Handle plugin-specific resources in TrackContainerView/ResourcePreviewer

Up to now plugin-specific resources (e.g. ZynAddSubFX presets) were
not previewed or loaded into a track container. This now works by
adding TypePluginSpecificResource to the according switch-block.

Signed-off-by: Tobias Doerffel <tobias.doerffel@gmail.com>

src/core/ResourcePreviewer.cpp

@@ -94,6 +94,7 @@ void ResourcePreviewer::preview( ResourceItem * _item )
 			break;
 		case ResourceItem::TypeSample:
 		case ResourceItem::TypeSoundFont:
+		case ResourceItem::TypePluginSpecificResource:
 		{
 			// restore default settings we are going to preview a
 			// sample (which should be played at a default

src/gui/track_container_view.cpp

@@ -420,6 +420,7 @@ void trackContainerView::dropEvent( QDropEvent * _de )
 		break;
 	case ResourceItem::TypeSample:
 	case ResourceItem::TypeSoundFont:
+	case ResourceItem::TypePluginSpecificResource:
 		action.loadByPlugin(
 			dynamic_cast<instrumentTrack *>(
 				track::create( track::InstrumentTrack,