As the title says.
By the way, this (partially) refactors sage.misc.misc.repr_lincomb and its use in FreeAlgebra and friends. It also discards some now useless code in symmetric functions.
Depends on #12490
CC: @sagetrac-sage-combinat
Component: combinatorics
Keywords: Cernay2012
Author: Nicolas M. Thiéry
Reviewer: Florent Hivert
Merged: sage-5.0.beta5
Issue created by migration from https://trac.sagemath.org/ticket/12484