mobile: call settings, request camera on iOS on call start (#701)

* mobile: call settings, request camera on iOS on call start

* refactor preferences

* fix typo

apps/ios/Shared/SimpleXApp.swift

@@ -21,6 +21,7 @@ struct SimpleXApp: App {
 
     init() {
         hs_init(0, nil)
+        UserDefaults.standard.register(defaults: appDefaults)
         BGManager.shared.register()
         NtfManager.shared.registerCategories()
     }