This commit follows up b6c5a2da08c08b4df45c0885ec2757a117d83dea
by serializing the user's thread memberships in these cases:
1. When we do the initial channel fetch with messages, we get
all threads and all the user's thread memberships for those
messages.
2. When the thread list is fetched, we get all the user's memberships
in that list.
3. When the single thread is fetched, either from opening it from
the list, an OM indicator, or just from doing .find() on the
manager when a new MessageBus message comes in
This will let us track the lastReadMessageId on the client, and
will also let us fix an issue where the unread indicator in the
channel header was incrementing for every thread that got a
new message, regardless of whether the user was a member.
This commit adds the thread index and individual thread
in the index list unread indicators, and wires up the message
bus events to mark the threads as read/unread when:
1. People send a new message in the thread
2. The user marks a thread as read
There are several hacky parts and TODOs to cover before
this is more functional:
1. We need to flesh out the thread scrolling and message
visibility behaviour. Currently if you scroll to the end
of the thread it will just mark the whole thread read
unconditionally.
2. We need to send down the thread current user membership
along with the last read message ID to the client and
update that with read state.
3. We need to handle the sidebar unread dot for when threads
are unread in the channel and clear it based on when the
channel was last viewed.
4. We need to show some indicator of thread unreads on the
thread indicators on original messages.
5. UI improvements to make the experience nicer and more
like the actual design rather than just placeholders.
But, the basic premise around incrementing/decrementing the
thread overview count and showing which thread is unread
in the list is working as intended.
