Align project files with CodeHarbor

Since both projects are developed together and by the same team, we also want to have the same code structure and utility methods available in both projects. Therefore, this commit changes many files, but without a functional change.

app/serializers/hash_as_jsonb_serializer.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+# stolen from https://github.com/rails/rails/issues/25894#issuecomment-777516944
+# this serializer can be used by a model to make sure the hash from a jsonb field can be accessed with symbols instead of string-keys.
+class HashAsJsonbSerializer
+  def self.dump(hash)
+    hash
+  end
+
+  def self.load(hash)
+    hash.is_a?(Hash) ? hash.deep_symbolize_keys : {}
+  end
+end