WFCORE-14 - add operations for manipulating list & map attributes

initial version, i want do do some more cleanup of apis for easier manipulating on side of write/read attribute handlers
See my comment at https://github.com/wildfly/wildfly-core/pull/206/files#diff-caff84f283fb9500ec241e826f3a2728R60 . If the PR I reference there isn't merged or if the model is cloned before updateModel is called, it's not an issue.