Also keeps the count in the $USER object up to date whenever the
user deletes or reads a notification.

When new notifications are generated for a live user by another user,
or on cron, the logged-in user's unread count is reloaded from the
database into the session either on hitting the inbox, or whenever
$USER is committed for some other reason.

The code to reload the background fields on commit of the LiveUser
object has been changed to ensure that it still works at upgrade time,
where the 'reload' column doesn't exist in the user table yet, but
*does* exist in the User object.

Change-Id: I9c9a81bf77d0927352902dee0d989d6122757b47
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>