The new film “Shiva Baby” combines the traditional, weeklong Jewish mourning period with a meshugenah love rectangle and overbearing family members. Hilarious and anxiety-inducing, the movie, written and directed by Emma Seligman is now out in select theaters and on demand, during Passover. “It’s like a sort of Jewish wake that lasts a week and for me, and for Reform Jews and specifically Ashkenazi Reform, it just feels like any other family event,” Seligman told the Daily News. “That feeling of community is so helpful when you’re mourning,” said the Canadian-born filmmaker, 25. “But for me, t…