Feature/support settings per device (#640)

* Optionally prevent deletion and mutation of "MutableListSetting" items

* Save server metadata per device

This makes it possible to e.g. have different settings on a desktop and a smartphone.

src/typings.ts

@@ -229,6 +229,10 @@ export type MetadataServerSettings = {
     showAddToLibraryCategorySelectDialog: boolean;
     ignoreFilters: boolean;
     removeMangaFromCategories: boolean;
+
+    // client
+    devices: string[];
+    activeDevice: string;
 };
 
 export interface ISearchSettings {