Display a notification when successfully installing a package

What do you guys think? If we add something like this we might also want to add a setting to disable it and maybe to toggle the sound, but I think it's pretty cool!

![screen shot 2013-05-15 at 1 04 44 am](https://f.cloud.github.com/assets/749864/504495/0002cec0-bceb-11e2-8a77-2c4ed9387867.png)