more work on synchronizing metadata with xmp sidecars

(cherry picked from commit 81bbff6e6ae87bd35e8050a1cc621297ca24939b)

rtengine/settings.h

@@ -1,4 +1,5 @@
-/*
+/* -*- C++ -*-
+ *  
  *  This file is part of RawTherapee.
  *
  *  Copyright (c) 2004-2010 Gabor Horvath <hgabor@rawtherapee.com>
@@ -112,6 +113,19 @@ public:
     };
     ThumbnailInspectorMode thumbnail_inspector_mode;
 
+    enum class XmpSidecarStyle {
+        STD, // FILENAME.xmp for FILENAME.ext
+        EXT  // FILENAME.ext.xmp for FILENAME.ext
+    };
+    XmpSidecarStyle xmp_sidecar_style;
+
+    enum class MetadataXmpSync {
+        NONE,
+        READ,
+        READ_WRITE
+    };
+    MetadataXmpSync metadata_xmp_sync;
+
     /** Creates a new instance of Settings.
       * @return a pointer to the new Settings instance. */
     static Settings* create();