Handle other message formats and chats without explicit titles.

[stuaxo]

• Handle other message formats (I think these used the web plugin).
• Handle chats with no title - infer it from the first line of the first message.

[stuaxo]

These were things that caused errors trying to import my conversations, with these fixes it gets through all the markdown files.

I haven't exhaustively tested whether the output looks correct.

[stuaxo]

Thanks @daugaard47

[daugaard47]

@stuaxo Thank you! I appreciate it!