Number field normalization

[fredrik-johansson]

ca_set_qqbar should try harder to standardize:

• Maybe sqrt(-3) -> exp(2 pi / 3) and sqrt(5) -> phi, etc. (like Pari does)
• For roots of unity, maybe standardize to exp(2 pi i /n)
• Make a choice when there is real/imaginary symmetry
• Always normalize to a monic polynomial
• After normalizing to a monic polynomial, use some more heuristics; at least try to find a linear transformation that minimizes content
• For low-degree polynomials, implement polredabs / polredbest
• Recognize cyclotomic and trigonometric fields at least in some cases (expensive at high degrees)