Song, InstrumentTrack: use DataFile::LocaleHelper

Always save projects and presets with default C locale in order to avoid
problems in the future. At the same time properly load floating point
strings which have been saved with different locale settings.

Closes #1051.

src/core/song.cpp

@@ -896,6 +896,8 @@ void song::loadProject( const QString & _file_name )
 		return;
 	}
 
+	DataFile::LocaleHelper localeHelper( DataFile::LocaleHelper::ModeLoad );
+
 	engine::mixer()->lock();
 
 	// get the header information from the DOM
@@ -1004,6 +1006,8 @@ void song::loadProject( const QString & _file_name )
 // only save current song as _filename and do nothing else
 bool song::saveProjectFile( const QString & _filename )
 {
+	DataFile::LocaleHelper localeHelper( DataFile::LocaleHelper::ModeSave );
+
 	DataFile dataFile( DataFile::SongProject );
 
 	m_tempoModel.saveSettings( dataFile, dataFile.head(), "bpm" );

src/tracks/InstrumentTrack.cpp

@@ -1369,6 +1369,8 @@ void InstrumentTrackWindow::saveSettingsBtnClicked()
 		!sfd.selectedFiles().isEmpty() &&
 		!sfd.selectedFiles().first().isEmpty() )
 	{
+		DataFile::LocaleHelper localeHelper( DataFile::LocaleHelper::ModeSave );
+
 		DataFile dataFile( DataFile::InstrumentTrackSettings );
 		m_track->setSimpleSerializing();
 		m_track->saveSettings( dataFile, dataFile.content() );