Add support for .pat previews, drag+drop

Closes #4202

src/gui/FileBrowser.cpp

@@ -424,7 +424,7 @@ void FileBrowserTreeWidget::mousePressEvent(QMouseEvent * me )
			m_previewPlayHandle = s;
			delete tf;
		}
		else if( ( f->extension ()== "xiz" || f->extension() == "sf2" || f->extension() == "gig" ) &&
		else if( ( f->extension ()== "xiz" || f->extension() == "sf2" || f->extension() == "gig" || f->extension() == "pat" ) &&
			! pluginFactory->pluginSupportingExtension(f->extension()).isNull() )
		{
			m_previewPlayHandle = new PresetPreviewPlayHandle( f->fullName(), f->handling() == FileItem::LoadByPlugin );
@@ -489,6 +489,10 @@ void FileBrowserTreeWidget::mouseMoveEvent( QMouseEvent * me )
					new StringPairDrag( "soundfontfile", f->fullName(),
							embed::getIconPixmap( "soundfont_file" ), this );
					break;
				case FileItem::PatchFile:
					new StringPairDrag( "patchfile", f->fullName(),
							embed::getIconPixmap( "sample_file" ), this );
					break;
				case FileItem::VstPluginFile:
					new StringPairDrag( "vstpluginfile", f->fullName(),
							embed::getIconPixmap( "vst_plugin_file" ), this );

src/gui/TrackContainerView.cpp

@@ -340,7 +340,7 @@ void TrackContainerView::dragEnterEvent( QDragEnterEvent * _dee )
{
	StringPairDrag::processDragEnterEvent( _dee,
		QString( "presetfile,pluginpresetfile,samplefile,instrument,"
				"importedproject,soundfontfile,vstpluginfile,projectfile,"
				"importedproject,soundfontfile,patchfile,vstpluginfile,projectfile,"
				"track_%1,track_%2" ).
						arg( Track::InstrumentTrack ).
						arg( Track::SampleTrack ) );
@@ -378,7 +378,8 @@ void TrackContainerView::dropEvent( QDropEvent * _de )
		_de->accept();
	}
	else if( type == "samplefile" || type == "pluginpresetfile" 
		|| type == "soundfontfile" || type == "vstpluginfile")
		|| type == "soundfontfile" || type == "vstpluginfile"
		|| type == "patchfile" )
	{
		InstrumentTrack * it = dynamic_cast<InstrumentTrack *>(
				Track::create( Track::InstrumentTrack,