If you had an inaccurate unread count due to previously broken unread
tracking, it's possible to go negative and never fully recover. Fixed
by clamping to zero.
// FREEBIE
Messages that are received in the active conversation while the window
is focused, are automatically marked as read.
The conversation appears as unread for a split second as the incoming message
arrives but it gets marked as read as soon as the message is displayed.
Fixed the global counting of unread messages. This makes the "unreadCount"
variable in storage to stay in sync with the sum of unread messages in each
conversation. To achieve this, the controller_view updates the global
variable whenever messages are received or read.
Encapsulate the global conversation cache collection against accidental
access, avoiding the data-clobbering bug fixed in previous commit.
Also move some one-off program initialization code from panel controller
to background.js
// FREEBIE
