Add web app model, service to fetch metadata

spec/factories/app_catalog/web_apps.rb

@@ -0,0 +1,14 @@
+FactoryBot.define do
+  factory :app_catalog_web_app, class: 'AppCatalog::WebApp' do
+    url { "https://myfavoritedrinks.remotestorage.io/" }
+    name { "My Favorite Drinks" }
+    short_name { "Drinks" }
+    description { nil }
+    theme_color { nil }
+    background_color { nil }
+    display { nil }
+    start_url { nil }
+    scope { nil }
+    share_target { nil }
+  end
+end

spec/models/app_catalog/web_app_spec.rb

@@ -0,0 +1,5 @@
+require 'rails_helper'
+
+RSpec.describe AppCatalog::WebApp, type: :model do
+  pending "add some examples to (or delete) #{__FILE__}"
+end