add hreflang tag feature

[bnchdrff]

this PR adds a feature to support the hreflang link tag so search engines can see other versions of the same product URL -- this is useful for stores with a store view for each language/region.

also it fixes (what i think is) a bug in composer.json that prevents it from working with a project that used the magento starter package.

finally there's a fix for a bug i ran into where product category info is not available.

i can split these into multiple PRs if that makes more sense!