optimize number field arithmetic using flint and singular

[was]

This should be broken into smaller tickets. See:

• #9400 -- discriminant bound
• #9752 -- sorting

[spancratz]

C code for rational polynomials based on FLINT1

[was]

basic refactoring of number fields elements -- only arithmetic with absolute fields works now.

[spancratz]

Including basic support for flint

[was]

flattened of everything. apply only this.

[was]

I will start posting part1, part2, etc. Then when all is done, a flattened version of it all.

[malb]

Note to self: turn cdef poly* normal_form(self, poly* p) into a singular_polynomial_normal_form() function to make it easier to use.

[was]

I've decided not to work on this further anytime soon. If somebody else wants to take it up, that would be fantastic.