Lenovo has announced a new entry in its ThinkCentre all-in-one line, the ThinkCentre Edge 91z. Aimed at small and medium-sized businesses, the system measures just 2.5 inches thick, offers a 21.5-inch LCD display, and packs a lot of power—up to a second-generation Intel Core i7 quad-core processor. The 91z supports up to 8 GB of…