unity package missing depends on python-gobject

[Oded Arbel]

on xenial, python-gobject isn't installed when installing unity, but /usr/bin/unity does `import glib` which fails without python-gobject.

Also, `apt-get remove python-gobject` doesn't complain about unity dependency but breaks unity.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: unity 7.4.0+16.04.20151102-0ubuntu2
ProcVersionSignature: Ubuntu 4.2.0-19.23-generic 4.2.6
Uname: Linux 4.2.0-19-generic x86_64
ApportVersion: 2.19.2-0ubuntu8
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CurrentDesktop: Unity
Date: Mon Nov 30 01:48:01 2015
InstallationDate: Installed on 2015-11-29 (0 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20151129)
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)