Sunday was Courtny Gerrish's last night on Channel 6. She's departing for the bright lights of Milwaukee, where she'll anchor the late afternoon news. To understand why she's leaving, we think it'd be fun to imagine the conversation that must have taken place nearly a year ago, when Gerrish was hoping to fill the anchor vacancy on the Big Six's 4 p.m. newscast. If WOWT GM Frank Jonas and News