Previously, HomeModel could listen to all subscriptions throughout the
app, and it would handle reaction and repost counting.
Once moved to the local relay model, HomeModel no longer had access to
all subscriptions, causing those counts to disappear.
The issue was fixed by doing the counting from ThreadModel itself, which
better isolates concerns throughout the app.
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>