Named both for its unusual location—on the seventh floor of downtown Chicago’s historic Garland Building, which was built in the early 1900s—and for the aromas and tastes that greet diners, Heaven On Seven has been serving Cajun fare for decades. It’s most distinctive feature, though, are the hot sauces that cover the tables and even the walls. The restaurant did not feature a hot-sauce collection when chef-owner Jimmy Bannos and his family took over the eatery in 1980, which served Jewish deli foods. But when a cousin married into a family…