clean up slf4j dependencies
 - tiles should declare slf4j-api as depedency to be included transitively since its code references it,
 - tiles should not declare at all any slf4j implementation dependency in compile or runtime scope,
 - include in all test scopes sl4j-simple


git-svn-id: https://svn.apache.org/repos/asf/tiles/request/branches/TREQ_1_0_X@1583196 13f79535-47bb-0310-9956-ffa450edef68