This means that all content models will now come from the same source to remove duplication across multiple models and `chatbarcaches`.
It also handily breaks the dependency on needing `MessageContentModel` for `NeochatRoom`
This is mostly just for text type messages at the moment but give the framework so that when other message types can be sent in threads they can be added easily
Create Message attached property to propagate parameters like room, timeline, index and maxContentWidth down to the message content avoiding lots of boilerplate