Support for notifications

[RyanTG]

If you get a response from the API that has a "notification" tag, pop up that notification.

I think Scott can clarify how this should be implemented.

[scottwainstock]

@RyanTG Uhh... I'm working on this right now, but I kind of lost some of the context for why we wanted it. I know it came up during the recent trouble with the iOS app, but I couldn't remember what our goal here is. WHAT IS OUR GOAL.

[RyanTG]

I think the goal is mostly to provide contextual error messages. Use: someone tries to add a machine, but it doesn't work. they receive a message saying "sorry, that machine couldn't be added. try again later." or something.

We might have had other, similar goals, too. I'll try to think of them.