Import/export chat styles

ts/model-types.d.ts

@@ -329,6 +329,11 @@ export type ConversationAttributesType = {
   conversationColor?: ConversationColorType;
   customColor?: CustomColorType;
   customColorId?: string;
+
+  // Set at backup import time, exported as is.
+  wallpaperPhotoPointerBase64?: string;
+  wallpaperPreset?: number;
+
   discoveredUnregisteredAt?: number;
   firstUnregisteredAt?: number;
   draftChanged?: boolean;