At long last, the big DC TV four night crossover event is finally here. Supergirl got it started Monday by, um, having a completely standalone episode which made time for a one-minute cameo from Barry and Cisco at the end (a cameo that was then repeated almost in its entirety on The Flash). Okay. Maybe the CW has been overhyping this just a little bit. Turns out, this is really just a three-night crossover event beginning with The Flash's "Invasion!" in which some cheap ...