This adds previews for downloaded pdfs and code files.
Move the itinerary model representation to it's own component and instantiate from MessageComponentModel. This starts to lay some groundwork for previewing other files.
The aim is to be able to use separate delegate for things like codeblocks and quotes so that they can be styled differently.
For now everything should look identical. However this moves to using a model for the content of the message and is intended to lay the foundation for improved message content representation, e.g. splitting up a text message in multiple sections and using different delegates for things like code and quotes.
