The retail industry is beginning to look like a barbell, with significant growth at the top and bottom of the spectrum while the middle gets squeezed out. On one end, you have discount retailers like the TJX Companies Inc. NYSE: TJX, reporting record revenue and terrific stock gains. Conversely, high-end outlets and brands like ULTA Beauty Inc. NASDAQ: ULTA and Kate Spade are producing strong sales while maintaining comfortable margins. And then in the middle, you have Target Corp. NYSE: TGT.Get Williams-So ...