Our threads now also contain all replies to their sub-threads.
This is similar to how sections work in MediaWiki, where the parent
section also contains the content of all the lower-level sections.
We're going to need this for notifications about replies in a thread.
Bug: T264478
Change-Id: I241fc58e2088a7555942824b0f184ed21e3a8b6f
Previously, only comments could have IDs, because we only needed IDs
for replying. But we might also use them for notifications soon.
Bug: T264478
Change-Id: I1bcad02bf17ab54bc5028a959543c10f0430836b
I haven't really reviewed the outputs, but at least a) they don't
crash b) they will fail if the output suddenly changes (which could
cause problems due to caching).
Bug: T252555
Change-Id: I1bbcbc5dd17ce1e24b3622062f5e8df4baf5f389
