[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

src/modules/welcome/WelcomePage.h

@@ -46,6 +46,8 @@ public:
     /// @brief Results of requirements checking
     bool verdict() const;
 
+    /// @brief Change the language from an external source.
+    void externallySelectedLanguage( int row );
 protected:
     void focusInEvent( QFocusEvent* e ) override; //choose the child widget to focus
 

src/modules/welcome/WelcomeViewStep.cpp

@@ -161,5 +161,11 @@ WelcomeViewStep::setCountry( const QString& countryCode )
         return;
     }
     else
-        cDebug() << "Would like to select" << c_l;
+    {
+        int r = CalamaresUtils::Locale::availableTranslations()->find( countryCode );
+        if ( r < 0 )
+            cDebug() << "Unusable country code" << countryCode << "(no suitable translation)";
+        if ( ( r >= 0 ) && m_widget )
+            m_widget->externallySelectedLanguage( r );
+    }
 }