builder: Add an option to erase app dir
builder: Add an option to erase app dir

Having to run rm -rf yourself before every new build attempt
gets old. Lets add an option to have xdg-app-builder do it
for us.

matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/xdg-app,flatpak/flatpak,amigadave/flatpak,GeorgesStavracas/flatpak,handsome-feng/flatpak,matthiasclasen/xdg-app,GeorgesStavracas/flatpak,handsome-feng/flatpak,alexlarsson/xdg-app,handsome-feng/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,alexlarsson/xdg-app,flatpak/flatpak,GeorgesStavracas/flatpak,matthiasclasen/xdg-app,matthiasclasen/flatpak,handsome-feng/flatpak,amigadave/flatpak,flatpak/flatpak,alexlarsson/xdg-app,matthiasclasen/flatpak,GeorgesStavracas/flatpak,amigadave/flatpak,GeorgesStavracas/flatpak,matthiasclasen/xdg-app,flatpak/flatpak,amigadave/flatpak,matthiasclasen/flatpak,alexlarsson/xdg-app