Sticky notifications in notification center

[phuhl]

From #111

I'm eventually having thoughts that go against your design approach. But I like the notification and applet center of OS X. I kinda dislike to have such information like next calendar meeting or current music track in the status line. But having plain notifications that always pop-up and disappear are also not a nice solution. Taking the music as an example, I think it is more like you actively want to know the current track at a specific point in time rather then you want to get notified all the time with shortly shown messages. But the event based approach (as notifications work...) and your great design are appealing to kind of pushing updates as notifications that always replace the last notification of the same tool (like music or calendar). But even they would not pop-up and only show up in the notification center, they would still get pushed down by other notifications, are always displayed at a different location or just disappear at the bottom of the screen. Therefore I'm asking about the stickyness.