debian: Update the Vcs-* URLs

Now that we have a working and up to date repository on Alioth, use
those URLs instead of my private repository.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>
debian: Update the package descriptions

Updated all package descriptions based on the upstream text, which is
also used for other distribution packages.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>