Bug#1115535: gnome-flashback: create a metapackage

[Jeremy Bícha]

Source: gnome-flashback
Version: 3.56.0-1

Please create a metapackage for gnome-flashback.
task-gnome-flashback-desktop could depend on this new metapackage
similar to how task-gnome-flashback depends on the gnome-core
metapackage. This would allow you to have more control over what gets
installed when someone chooses GNOME Flashback in the Debian
Installer.

Thank you,
Jeremy Bícha