[packagechooser] Look for screenshots in more places.

It is easier to put screenshots somewhere where
they can be searched-for, rather than requiring either
absolute paths (inconvenient to try out someone's
settings) or relative paths (because who knows where
Calamares will be run during testing).

src/modules/packagechooser/PackageModel.cpp

@@ -9,15 +9,28 @@
 
 #include "PackageModel.h"
 
+#include "Branding.h"
 #include "utils/Logger.h"
 #include "utils/Variant.h"
 
-static QPixmap loadScreenshot( const QString& path )
+#include <QFileInfo>
+
+static QPixmap
+loadScreenshot( const QString& path )
+{
+    if ( QFileInfo::exists( path ) )
     {
-    cDebug() << path;
         return QPixmap( path );
     }
 
+    const auto* branding = Calamares::Branding::instance();
+    if ( !branding )
+    {
+        return QPixmap();
+    }
+    return QPixmap( branding->componentDirectory() + QStringLiteral( "/" ) + path );
+}
+
 PackageItem::PackageItem() {}
 
 PackageItem::PackageItem( const QString& a_id, const QString& a_name, const QString& a_description )

src/modules/packagechooser/packagechooser.conf

@@ -95,7 +95,11 @@ labels:
 #       Human-readable description. These can be translated as well.
 #  - *screenshot*
 #       Path to a single screenshot of the product. May be a filesystem
-#       path or a QRC path, e.g. ":/images/no-selection.png".
+#       path or a QRC path, e.g. ":/images/no-selection.png". If the path
+#       is not found (e.g. is a non-existent absolute path, or is a relative
+#       path that does not exist in the current working directory) then
+#       an additional attempt is made to load the image from the **branding**
+#       directory.
 #
 # The following field is **optional** for an item:
 #