Tensions between Whole Foods Market and some of the most important brands it sells in its stores will come to head on March 19. The grocer notified certain vendors about the meeting last Saturday. A key issue discussed will be Whole Foods' efforts to centralize its merchandising. Tensions between Whole Foods Market and some of the most important brands it sells in its stores will come to a head on March 19, when they will congregate for a recently announced summit, sources familiar with the situation tell CNBC. The grocer notified certain vendors about the meeting by email last Saturday....