sci-mathematics/cliquer: new package of graph clique-finding routines.

sci-mathematics/cliquer: new package of graph clique-finding routines.

This is a straightforward import of the cliquer package from the
sage-on-gentoo overlay, where it was maintained by François Bissey,
with minor changes:

  * Update to EAPI=7.
  * Add the original cliquer homepage to HOMEPAGE.
  * Use the SageMath upstream tarball and drop autotools.eclass.

Technically we are packaging Dima Pasechnik's "autocliquer" fork of
cliquer, but the only difference between the two is an autotools build
system that makes our lives oh so much easier.

Closes: https://bugs.gentoo.org/707522
Package-Manager: Portage-2.3.84, Repoman-2.3.20
Signed-off-by: Michael Orlitzky <mjo@gentoo.org>