icon browser: Add some dnd support

Use a custom tree model and enable dragging from the icon view.
Currently, we just support dropping the icon name as text.

demos/icon-browser/iconstore.h

@@ -0,0 +1,26 @@
+#ifndef __ICON_STORE_H
+#define __ICON_STORE_H
+
+#include <gtk/gtk.h>
+
+
+#define ICON_STORE_TYPE (icon_store_get_type ())
+#define ICON_STORE(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), ICON_STORE_TYPE, IconStore))
+
+
+typedef struct _IconStore       IconStore;
+typedef struct _IconStoreClass  IconStoreClass;
+
+enum {
+  ICON_STORE_NAME_COLUMN,
+  ICON_STORE_SYMBOLIC_NAME_COLUMN,
+  ICON_STORE_DESCRIPTION_COLUMN,
+  ICON_STORE_CONTEXT_COLUMN
+};
+
+GType   icon_store_get_type     (void);
+
+void    icon_store_set_text_column (IconStore *store,
+                                    gint       column);
+
+#endif /* __ICON_STORE_H */