add a option to align columns in a matrix other that "right"
Trac #16267: option to change column alignment in a matrix (in LaTeX output)

At the moment all columns are aligned on the right. This should be more
flexible and allowing center and left as well.

URL: http://trac.sagemath.org/16267
Reported by: dkrenn
Ticket author(s): Daniel Krenn
Reviewer(s): Clemens Heuberger