Update unreadCounts per-conversation on incoming messages. Render unread
conversations with font-weigh: bold in the inbox view.
To ensure that the inbox and conversation views remain in sync, the
background page now ensures that the same models objects are used for
both views.
With these changes, message bubbles in the default-sized chat popup are
just wide enough to display the full complement of html5 media player
controls.
Previously the conversation window would query the background page
for a model id and then fetch the conversation. Instead, we can fetch
the conversation before opening the window, which simplifies the front
end scripts and avoids creating multiple copies of the same model.
