This MR is a cumulative one with 5 fixes including:
- Allow setting
preferred_langaugefor a MailingList. (Closes #303 (closed))
- Allow setting empty templates to get around the fact that we don't have a way to message decoration. (Closes #331 (closed), Closes #324 (closed))
- Expose all the digest settings from the REST API in Postorius. (Closes #211 (closed))
- Add a badge of held message and pending subscription requests. (Closes #308 (closed))
- Allow viewing, adding and removing Domain owners so it can be later used to allow them to create lists.
- Allow setting per-list member roster visibility options. (Closes #22 (closed))