[sldev] Notifications redesign

[Argent Stonecutter]

Well, speaking as someone who has been doing control system  
development for years, notifications (we call them alarms) are a Big  
Deal.

Typically in a control system you can:

* View current (unacknowledged) alarms in a list.
* View individual alarm details.
* Review recent acknowledged or unacknowledged alarms.
* Filter alarms.
* Acknowledge individual alarms, all displayed alarms (subject to  
filter), all non-critical alarms, and all alarms of an individual class.

I have long wished that computer software for desktops had these  
kinds of tools, rather than just displaying each individual  
notification as a separate dialog box. In SL, where you can have many  
many pending notification (unacknowledged alarms) this is even more  
critical.