ON THE ROAD AGAIN: It seems as if Orange County's arts community is in a constant state of flux. . . . Last month, country singer Jann Browne packed her bags and left for Nashville. Now, another local country stalwart, Patty Booker, has followed, though not for good. She and songwriting collaborator Gary Brandin are headed to Nashville to record demonstration tapes. Booker says: "We want to keep our basic sound, but we're willing to be realistic and work with them."