This PR introduces thread support for channel archives. Now, threaded messages are rendered inside a `details` HTML tag in posts.
The transcript markdown rules now support two new attributes: `threadId` and `threadTitle`.
- If `threadId` is present, all nested `chat` tags are rendered inside the first one.
- `threadTitle` (optional) defines the summary content.
```
[chat threadId=19 ... ]
thread OM
[chat ... ]
thread reply
[/chat]
[/chat]
```
If threads are split across multiple posts when archiving, the range of messages in each part will be displayed alongside the thread title. For example: `(message 1 to 16 of 20)` and `(message 17 to 20 of 20)`.
ac9e804dbe