Gwen Yip’s “Rainy Day” is part of “The Maximum Minimum,” an exhibit at The Gallery Space in Rahway. All storytellers know this: What is omitted is just as important as what is included. Some details sing, some provide context, and some are best left out altogether. A good artist sidesteps distractions and directs the attention of her audience to the emotionally resonant elements of her work. This knack is especially crucial for storytelling painters, who generally have no more than a single panel to make an impression. Yet when it is done right, a painting can imply a rich narrative, fire the …