Create the classes of univariate polynomials over number fields
Add gcd method to polynomial_number_field using pari
Use proper constructions for the library. Minor fixes in other parts of the code.
Merge branch 'master' into u/lftabera/gcd_number_field_pari
#15475: doc fixes after #10963
Fixed resultant for polynomials over function fields.

Polynomials over extensions of rational function fields can not be converted to
PARI. Now an appropriate exception is raised.
Also, if the order of the variables is not like PARI expects it, then a
PariError is raised. If this happens, rely on the naive implementiation, i.e.,
compute the determinant of the Sylvester matrix.
Merge branch 'public/categories/15475' of trac.sagemath.org:sage into public/categories/15475
Implemented _coerce_map_from_ for SGA.
More fixes and doctests.
Fixed the issue...finally... Also some other minor cleanup.
Added comment about register_embedding.
Changed to use _coerce_map_from_ and made it more robust/general.
documentation fixes to canonical_embedding of symmetric group algebra (yes, these maps aren't always embeddings, and the inequality was backwards)
oops, another doc fix
Merge commit 'ff4e546a838e9e9a4be86b3a89d8596658beb3f4' into public/coercions/fix_sga_coercions-16678
Additional fixes noted on sage-devel thread.

This improves interaction between Permutation, SymmetricGroup
and SymmetricGroupAlgebra. This also puts the SGA into a better
category.
Fixed stupid mistake.
Removed erroneous character in permgroup.py.
a couple doctests and a blunder of my own
trac #16700 correct latex of bimodules