[welcome] Lookup GeoIP language and pass to language widget

- FIXES #934
 - Whether this is really wanted depends on the distro, and I'm not
   100% convinced the likely tags from Unicode are correct (or it'd
   take a lot more data). In any case, starting Calamares in "NL"
   gets me "nl_NL" as translation; presumably starting it in "BE"
   will get me that as well (what about Les Wallons?)
 - This also shows off that it's a real hack to have so much program
   logic in the *widget* parts of each ViewStep. Longer-term,
   a lot of functionality should go to the ViewStep itself, which
   will then control the UI.

src/modules/welcome/WelcomePage.cpp

@@ -257,11 +257,19 @@ WelcomePage::focusInEvent( QFocusEvent* e )
     e->accept();
 }
 
-bool WelcomePage::verdict() const
+bool
+WelcomePage::verdict() const
 {
     return m_checkingWidget->verdict();
 }
 
+void
+WelcomePage::externallySelectedLanguage( int row )
+{
+    if ( ( row >= 0 ) && ( row < ui->languageWidget->count() ) )
+        ui->languageWidget->setCurrentIndex( row );
+}
+
 
 void
 LocaleTwoColumnDelegate::paint(QPainter* painter, const QStyleOptionViewItem& option, const QModelIndex& index) const