Tonight's Neighborhood Advisory Group meeting could flare up over ongoing conflicts between two opposing groups. At the same time, Marshall Park neighbors and other residents will look to the city for answers after violence broke out outside J Street bars and outdoor concerts were held over the weekend without notice to residents, just weeks after controversial Midfest and Cinco de Mayo events. The two groups -- organized neighborhood association members and business interests -- have tried in the past to work out differences involving the neighborhood impacts of a block of J Street bars and restaurants. More problems and concerns arose over special events held in the area in May. Now a