The Center for the Arts just announced two more big shows for spring. Grammy-award winning composer Chick Corea will grace the Grass Valley stage April 30 with his band The Vigil. Then May 18, outspoken comedian, singer and social commentator Sandra Bernhard will perform in the 300-seat venue on West Main Street. Tickets for both shows go on sale to members of the Center Wednesday. They will be available to the general public Feb. 14. Sinceembarking on a solo career in 1966, Chick has been at the forefront of jazz, both as a renowned pianist forging new ground with his …