Allow flatpak to satisfy the bubblewrap dependency again
now that flatpak 0.8 has been considered a stable base https://blogs.gnome.org/alexl/2016/12/22/a-stable-base-for-flatpak-0-8/ I think the sandboxed tor browser should allow flatpak-bwrap to satisfy the dependency of bubblewrap again (I am aware this was already present and was removed https://gitweb.torproject.org/tor-browser/sandboxed-tor-browser.git/commit/?id=1bdce61925564ca0c688377c196268ce97b5402b )
As there is a ppa for Ubuntu 16.06 LTS users by the flatpak main dev: https://launchpad.net/~alexlarsson/+archive/ubuntu/flatpak?field.series_filter=xenial
This solves the problem of Ubuntu users not being able to use the sandboxed tor browser without compiling bubblewrap from source or installing the package for ubuntu 17.04 (which is less than ideal, because either the user is breaking their systems by adding repositories they shouldn't, or they are installing bubblewrap by hand and will probably miss out on newer versions).