FEATURE: Import and export themes in a .tar.gz format (#6916)

lib/theme_store/tgz_importer.rb

@@ -14,6 +14,8 @@ class ThemeStore::TgzImporter
     Dir.chdir(@temp_folder) do
       Discourse::Utils.execute_command("tar", "-xzvf", @filename, "--strip", "1")
     end
+  rescue RuntimeError
+    raise RemoteTheme::ImportError, I18n.t("themes.import_error.unpack_failed")
   end
 
   def cleanup!
@@ -38,6 +40,12 @@ class ThemeStore::TgzImporter
     end
   end
 
+  def all_files
+    Dir.chdir(@temp_folder) do
+      Dir.glob("**/*").reject { |f| File.directory?(f) }
+    end
+  end
+
   def [](value)
     fullpath = real_path(value)
     return nil unless fullpath