Remove divisions in cdd

[MathieuDutSik]

LRS can process polytope and find the dual description without using any divisions. If one takes the LRS code and replace the mpz_class by mpq_class then we get a factor 3 in speed. Thus I think there is a big potential in speed increase for CDD by using arithmetic more cleverly. The routine where there are such divisions is dd_GaussianColumnPivot and this should be avoidable (other instances are easier to resolve).

Note: Templated versions of CDD and LRS are available on https://github.com/MathieuDutSik/polyhedral_common/tree/master/src_poly