MONDAY When Elizabeth Berg titled her novel We Are All Welcome Here, she wasn’t kidding—just about every Southern-fried device and pre-Vietnam social concern is stuffed into its pages. Polio, single-parent striving, racial prejudice, nosy Southern biddies, miraculous monetary windfalls, Elvis Presley, and, of course, plucky Southern Belles that survive as if they were…maybe some sort of tree made out of some sort of metal. Anyway, Berg will be on hand at the Rockville Barnes and…