Added Blacklist setting

Hi,

Nice package you have built, but I found myself in the need of preventing some packages from being updated automatically, so I added a **Blacklist** option.

In order to filter out packages I had to use `apm install` instead of `apm upgrade` (which does not take package names as an argument). Under the hood, apm `upgrade` uses `install` also. So right now, it is running `apm upgrade --list --json` to get a list of what updates are available and then filtering potential packages before running install.

Other than that, I have made a few CoffeeScript-cosmetic changes (feel free to neglect them) and display more human-friendly package names in the notification.

Have a good day!

PS. I have also updated the `README` if you feel like adopting it.