Bug 1030996 - Add in tool notifications

This is a draft for feedback
I did a bit of research and the consensus I inferred from a number of SO questions and blog posts was that overriding save was better. People seemed to suggest that if you don't _need_ a signal you shouldn't use one. My initial feeling was to use a signal, as that seems like what they're meant for, but I figured those with more experience than me knew better. 

Why would you choose to use a signal? Just so you don't have to override save?