Proposed fix for issue #173

This is a proposed fix for this issue. I'm putting this in a pull request because I do not have enough information about Notifications to know whether this is the best course of action or not. The proposed actions are these:

* Rename `Komanda.notification` to `Komanda.Notification`. Minor, the capitalization was just bothering me, since it is a constructor, after all.
* Rather than check if `window.Notification` is present, check instead that `Komanda.Notification` is. This is for  a couple of reasons, the main being that if something is preventing notifications from working despite their being present, we don't want to expose them. Further, we may eventually want to use our own Notification system with a similar API so why not allow that possibility.
* On Windows, where node-webkit appears to crash on the deferred execution of the notification (*not* the construction), do not enable `Komanda.Notification`.