Debian package for OpenStego v0.5.0 has been added in Sourceforge downloads.
Ubuntu (or any other Debian based distro) users can now just download that file and install by just double-clicking the icon for the downloaded ".deb" file. It can also be easily installed from command-line using:
$ sudo dpkg -i openstego-0.5.0-1.deb
Please let me know in case if anyone faces installation issues using this package.