Just as Dawson’s Market gets ready to move out of Rockville, Aldi is moving in. Nov. 1 is opening day for the German grocer, which has taken over the former H.H. Gregg space near Bed Bath & Beyond on Rockville Pike. Aldi, which plans to open 2,500 new U.S. stores in the next four years, is known for its low prices, private-label brands, intentionally limited product lines and random surprise “treasure hunt” items. Customers bring their own bags, pack their own groceries and even pay a (refundable) 25-cent fee to use the shopping carts. Recently Aldi announced a new focus on organic, vegetarian, takeout and ready-to-cook foods as it tries to do a better job of catering to American palates.