Review how or if user is told when the app changes allocation amounts

[lcreid]

Current the invoice allocation amount in the invoice screen changes based on constraints of the RTP and/or the amount of the invoice (see Issue #65). It was proposed in Issue #65, but we decided it wasn't clear what the best solution was, so we left it.

One of the tricks is that since we auto-correct the number, there's no clear indication from the user that they've seen the message, aside from providing a pop-up they have to dismiss (which might be a valid solution).