Updates to reflect db schema change

DB was updated with additional fields "availability" (I, W, N -- in
stock, waitlist, not in stock) and "size_short" (e.g. size = Small, but
size_short = S).

For availability, our previous implementation relied on the existence of
the key to determine availability.  Due to the DB change, all the keys
now exist, so we add another check for "I" status.

Not shown: updated form to include new "data-sizes" attribute storing a
json hash of sku_id/size_short mappings.  This allows us to parse the
size_short during init.