Various App Button improvements
WIP = really should write/fix some tests for this
The main change here is that PhoshAppButton now has a popover/menu containing the app's "Desktop Actions" (if any) and the option to add/remove from favourites
To implement this in a vaguely nice way I've moved favourite handling to a global singleton that mirrors the main app list. This also simplifies the app-grid as it can just bind to that model
Menu opens on right-click/menu-key on desktop and with touch input on long-press (and it even works on the devkit!)
Edited by Zander Brown