Support notification center

[cyberduck]

adc18bb created the issue

On OS X Mountain Lion (10.8), Apple introduces Notification Center, wish is much better than growl system.

The change is minimal, it requires a few (5) lines of code, or just one if create a method wrapper to Notification System.

[cyberduck]

@dkocher commented

Growl 2.0 now released routes messages to the Notification Center when running on 10.8.

[cyberduck]

@dkocher commented

In 43d4d19.