Support multiple taxons
Support multi-taxons for flat percent calculator
Promo on branch taxons affect children

Big changes:

Promotion rule no longer checks for taxon by name comparison.  Old
of this promotion should continue to work, but taxon names can no
longer be edited from admin.

When using the 'Flat percent of taxon total' calculator, you no
longer have to enter the taxon for that calculator.  If it is
blank, the calculator will use the taxons specified in the
associated taxon promotion rule.

Updated promo admin to new admin UI