[netinstall] Move translation of widget headers

Editorial: I really don't like plain CALAMARES_RETRANSLATE() thrown
into the middle of code.

src/modules/netinstall/NetInstallPage.cpp

@@ -41,6 +41,7 @@ NetInstallPage::NetInstallPage( QWidget* parent )
     , m_groups( nullptr )
 {
     ui->setupUi( this );
+    CALAMARES_RETRANSLATE_SLOT( &NetInstallPage::retranslate );
 }
 
 NetInstallPage::~NetInstallPage()
@@ -49,6 +50,16 @@ NetInstallPage::~NetInstallPage()
     delete m_reply;
 }
 
+void
+NetInstallPage::retranslate()
+{
+    if ( m_groups )
+    {
+        m_groups->setHeaderData( 0, Qt::Horizontal, tr( "Name" ) );
+        m_groups->setHeaderData( 1, Qt::Horizontal, tr( "Description" ) );
+    }
+}
+
 bool
 NetInstallPage::readGroups( const QByteArray& yamlData )
 {
@@ -62,8 +73,6 @@ NetInstallPage::readGroups( const QByteArray& yamlData )
         }
         Q_ASSERT( groups.IsSequence() );
         m_groups = new PackageModel( groups );
-        CALAMARES_RETRANSLATE( m_groups->setHeaderData( 0, Qt::Horizontal, tr( "Name" ) );
-                               m_groups->setHeaderData( 1, Qt::Horizontal, tr( "Description" ) ); )
         return true;
     }
     catch ( YAML::Exception& e )
@@ -125,6 +134,7 @@ NetInstallPage::dataIsHere()
         return;
     }
 
+    retranslate();  // For changed model
     ui->groupswidget->setModel( m_groups );
     ui->groupswidget->header()->setSectionResizeMode( 0, QHeaderView::ResizeToContents );
     ui->groupswidget->header()->setSectionResizeMode( 1, QHeaderView::Stretch );

src/modules/netinstall/NetInstallPage.h

@@ -64,6 +64,8 @@ public:
 public slots:
     void dataIsHere();
 
+    void retranslate();
+
 signals:
     void checkReady( bool );