(Reuters) - The city manager of Sanford, Florida, where a neighborhood watch leader shot and killed an unarmed teen, called a news conference on Thursday amid demands for an arrest in the case and a vote of no confidence for the police chief. The press conference at Sanford City Hall was called by City Manager Norton Bonaparte Jr., who was expected to discuss developments in the highly charged case. The killing of Trayvon Martin, 17, an African American, by neighborhood watch volunteer George Zimmerman, 28, a white Hispanic, has drawn national attention and sparked debate over Florida's "Stand Your Ground"...