It didn't take long for residents, young and old, to line up to paint their own personal tile, representing their view of the region's ecology or cultural history.   In classrooms, senior centers, and at community gatherings they painted images for featured murals along the Blue Line Trail.   Designed by California eco-artist Susan Steinman, a pioneer in ecological and cultural restoration public art, a mural on the side of the large blue building represents a quilt of experience, young and old, real and imagined.   Her second mural announces the entryway onto the Cantrell Bridge.