Add "Open containing folder" (#5453)

Add functionality to open the containing folder of a file that's selected
in LMMS' file browser.

Technical details
------------------
Add a new private method openContainingFolder to FileBrowser. Add a new
action to the context menu of a selected file. This action in turn calls
the added method.

The current implementation of openContainingFolder delegates to
QDesktopServices::openUrl with the directory of the selected file. Please
note that this will only open the directory but not select the file as
this is much more complicated due to different implementations that are
needed for the different platforms (Linux/Windows/MacOS).

Using QDesktopServices::openUrl seems to be the most simple cross
platform way which uses functionality that's already available in Qt.

include/FileBrowser.h

@@ -125,6 +125,7 @@ private slots:
 	void activateListItem( QTreeWidgetItem * item, int column );
 	void openInNewInstrumentTrackBBE( void );
 	void openInNewInstrumentTrackSE( void );
+	void openContainingFolder();
 	void sendToActiveInstrumentTrack( void );
 	void updateDirectory( QTreeWidgetItem * item );
 

src/gui/FileBrowser.cpp

@@ -24,6 +24,7 @@
  */
 
 
+#include <QDesktopServices>
 #include <QHBoxLayout>
 #include <QKeyEvent>
 #include <QLineEdit>
@@ -380,6 +381,11 @@ void FileBrowserTreeWidget::contextMenuEvent(QContextMenuEvent * e )
 								"B+B Editor" ),
 						this,
 					SLOT( openInNewInstrumentTrackBBE() ) );
+		contextMenu.addSeparator();
+		contextMenu.addAction( QIcon(embed::getIconPixmap( "folder" )),
+					tr( "Open containing folder" ),
+					this,
+					SLOT( openContainingFolder() ) );
 		contextMenu.exec( e->globalPos() );
 		m_contextMenuItem = NULL;
 	}
@@ -671,6 +677,16 @@ void FileBrowserTreeWidget::openInNewInstrumentTrackSE( void )
 
 
 
+void FileBrowserTreeWidget::openContainingFolder()
+{
+	if (m_contextMenuItem)
+	{
+		QFileInfo fileInfo(m_contextMenuItem->fullName());
+		QDesktopServices::openUrl(QUrl::fromLocalFile(fileInfo.dir().path()));
+	}
+}
+
+
 
 void FileBrowserTreeWidget::sendToActiveInstrumentTrack( void )
 {