Unity as depends in ubuntu-desktop (LP: #683833)

[Jonathan Carter (highvoltage)]

Hi!

In Edubuntu, we need to make Unity an optional installation rather than
by default. Unity is already an installation option from the installer
via a Ubiquity plugin, we're sticking with the classic desktop by
default since it's better suited for LTSP and currently offers better
usability.

Unity is currently marked as depends in ubuntu-desktop, which
edubuntu-desktop depends on. If it were marked as recommends it should
allow Edubuntu to ship it and only install it if the user selects it,
without negatively affecting anything else.

Bug report:
https://bugs.launchpad.net/ubuntu/+source/ubuntu-meta/+bug/683833

-Jonathan