[libcalamaresui] Store the slideshow-from-images data

- This code has existed for a long time but never stored anything
  to the Branding object, and the most literal slideshow (just some
  images) was not implemented.

src/libcalamaresui/Branding.cpp

@@ -238,7 +238,7 @@ Branding::Branding( const QString& brandingFilePath, QObject* parent )
                     slideShowPictures[ i ] = imageFi.absoluteFilePath();
                 }
 
-                //FIXME: implement a GenericSlideShow.qml that uses these slideShowPictures
+                m_slideshowFilenames = slideShowPictures;
             }
             else if ( doc[ "slideshow" ].IsScalar() )
             {

src/libcalamaresui/Branding.h

@@ -237,6 +237,16 @@ private:
     QMap< QString, QString > m_strings;
     QMap< QString, QString > m_images;
     QMap< QString, QString > m_style;
+
+    /* The slideshow can be done in one of two ways:
+     *  - as a sequence of images
+     *  - as a QML file
+     * The slideshow: setting selects which one is used. If it is
+     * a list (of filenames) then it is a sequence of images, and otherwise
+     * it is a QML file which is run. (For QML, the slideshow API is
+     * important).
+     */
+    QStringList m_slideshowFilenames;
     QString m_slideshowPath;
     int m_slideshowAPI;
     QString m_translationsPathPrefix;