chore(sofa): remove `sofa.inherits` method

this method isn't used anymore
feat(product): adds hasInfiniteStock method
feat(product): allow passing in a variant to calculate base price per variant
chore(dist): update dist files
chore(release): cutting 0.7.1 release
fix(Gruntfile): fixes license banner
fix(LICENSE): fixes naming
chore(*): release 0.7.2
fix(product): check for a valid unitAmount in getBasePriceStr
feat(grunt): easier deploying