added documentation for tensor products of crystals

[anneschilling]

added documentation for tensor products of crystals according to Daniel Bump's suggestions (conventions for tensor products in comparison with Kashiwara's conventions; tableaux)

CC: @sagetrac-sage-combinat

Component: combinatorics

Issue created by migration from https://trac.sagemath.org/ticket/4311

[sagetrac-mabshoff]

comment:1

Attachment: tensor-product-doc-trac.patch.gz

[mwhansen]

comment:2

Looks good to me.

[sagetrac-mabshoff]

comment:3

Merged in Sage 3.2.alpha0