Brian Steinberg Senior TV EditorJust as TV networks are starting to see new opportunities to snare much-needed ad cash, their digital competitors are going after the money as well.Roku, the popular streaming-video interface, will on June 22 kick off a series of presentations to advertisers from digital companies known as the “NewFronts.” In a more typical year, the “NewFronts” take place before a series of “upfronts,” or Madison Avenue showcases from TV networks.