Polynomial solver should also be improved

[WhiteBlackGoose]

Now it returns awful responses for 3+ degree polynomials where WA sometimes can return a neat set. We should somehow check if some constants could be those roots (say, check a few integer, a few rational, a few variables, etc.)

[MomoDeve]

what about Rational root theorem? For many simple cases we can go through all factors of the free term of polynomial to find exact roots