Visibility Labels: support visibility labels for user groups.

VisibilityClient API and shell commands can be used to grant and clear visibility authorizations of a group. e.g. set_auths '@group1', ['SECRET','PRIVATE'] get_auths '@group1' clear_auths '@group1', ['SECRET','PRIVATE'] When checking visibility authorizations of a user, the server will include the visibility authorizations of the groups of which the user is a member, together with the user's own. On the other hand, get_auths 'user1' will only get user1's own visibility authorizations. clear_auths 'user1' will only clear user1's own visibility authorizations. The visibility authorizations of a group can be changed by invoking the API or command on the '@group1' itself. Note: The following two methods have been deprecated in VisibilityLabelService from 0.98.10 and will be removed in 2.0+ releases. getAuths(byte[], boolean) havingSystemAuth(byte[]) Use the following methods instead: getUserAuths(byte[], boolean) getGroupAuths(String[], boolean) havingSystemAuth(User)