Add 'minibox' sandbox tool for use when running things like zip/unzip on user data.
Use 'minibox' to sandbox zip/unzip for backup/restore.

This also allows us to avoid the copies we were doing before, which lets us drop the fs-extra package. I already had a recursive-rmdir implementation. It's synchronous, but that seems OK for now.
After deleting a grain, return to home screen. Fixes #31.
Merge branch 'master' of github.com:sandstorm-io/sandstorm