[suggestion] Back button behavior

I'm talking about the smartphone's Back button and how it affects Quire.

When I'm editing a task, and press the back button, it usually means I changed my mind and would like to cancel the change, like saying "go back to where I was". Instead, currently quire suggests "Press back again to exit the app".

I think this should be changed. If in the middle of an action that offers a Cancel option, Back should activate Cancel. If not in the middle of such action, Back should suggest "press again to exit app".