Add a loop argument to simplify_full

[eviatarbach]

simplify_full should have a loop argument, which would continue simplifying until it is no longer possible. See http://ask.sagemath.org/question/1480/simplify-trig-abs-and-sqrt-expression for a possible implementation.

CC: @kcrisman

Component: symbolics

Issue created by migration from https://trac.sagemath.org/ticket/13099

[jasongrout]

comment:3

#2662 is related.