FAR OUT: OK, so they believe in UFOs. That doesn't mean that the Mutual UFO Network is a bunch of kooks, says John Weigle of the group's Ventura County chapter. "We just think there's something out there, we don't know what it is, and it's worthy of study." The 2 1/2-year-old chapter, which meets tonight at the Camarillo Library, is training people to investigate UFO sightings. . . . Members come from all walks of life except one: "We don't have a lot of scientifically trained people--no engineers or scientists. There's some stigma, maybe."