Aiming to ride two crazes at once, T-Mobile USA will sell a tablet computer that can shoot 3-D videos, the Associated Press reports. The cell phone company said Wednesday that the “G-Slate” tablet from LG Electronics Inc. will be out this spring, but it didn’t say exactly when, or how much it would cost. The tablet will have an 8.9-inch screen and two cameras on the back, which together can capture 3-D, high-definition video. The tablet will come with red-blue 3-D glasses for 3-D viewing while shooting…