watcher_notify_queue table should not be storing messages

The watcher_notify_queue table stores a copy of each notification message text, subject, and destination email address in the database. This is not a good idea because:

1. If you are sending notifications on cron run, then the information can be wrong or out of date by the time it is sent. For example, the user changes their email address after the post is made but before the notification is sent. Or the admin changes the template.

2. Most of the text is redundant as it is just the message template repeated over and over with the tokens replaced.

Instead the table should just store the qid, uid, and other information necessary to construct the message (node id, comment id, operation i.e. an insert / update etc).

Fixing this may also make it easier to program watcher into not sending multiple messages for the same node when multiple comments are added because at the moment you have no way of knowing what each notification message in the table relates to (though it will not help after cron has been run).