Refactor plugin apps (#4780)

* Refactor plugins

* Add missing names to view models

* Cleanups

* Replace SalesAppBaseType by two interfaces

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Co-authored-by: Dennis Reimann <mail@dennisreimann.de>

BTCPayServer/Controllers/UIStoresController.Dashboard.cs

@@ -42,6 +42,8 @@ namespace BTCPayServer.Controllers
                 return View(vm);
 
             var userId = GetUserId();
+            if (userId is null)
+                return NotFound();
             var apps = await _appService.GetAllApps(userId, false, store.Id);
             foreach (var app in apps)
             {