Bug#851856: gnome-software: missing support for standalone Debian packages

[espectalll at kydara.com]

Package: gnome-software
Version: 3.22.4-1
Severity: important

Trying to open a .deb package will GNOME Software will return a "Sorry, this
did not work. The file is not supported." error. This is not the expected
behavior, and should instead load the package file, show at least its name and
description, and offer an option to install it.

-- System Information:
Debian Release: 9.0
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)