Add logic for saving session preferences (#17)

app/models/auth/User.model.js

@@ -13,6 +13,10 @@ class User extends AuthUser {
     static get schema() {
         return {...super.schema, ...{
             // other schema fields here
+            preferences: {
+                dark_mode: { type: Boolean, default: false },
+                default_page: String,
+            },
         }}
     }