Fix virtual packet conflicts

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
Update package lists

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
Add a customizable local package list

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
Update Skype optional dependencies

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
Improve user interface

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>