Move Groebner basis computation

[saschatimme]

Just discovered that here is a Groebner basis computation hidden. It would be probably interesting to get this into MultivariatePolynomials. What do you think?

[blegat]

It is not in MultivariatePolynomials because it is not required for doing algebraic manipulation of the polynomials using the Base operators.
This package includes the interface for Ideal/algebraic set/semialgebraic sets with a few default fallbacks. Groebner basis computation makes sense in the context of an ideal so it has been included here.
What would be the advantage of moving it to MultivariatePolynomials ?