[core] Add descriptive operationText to the audit log for user/group admin operations
Adds new "operationText" field to audit log that includes corresponding user/group names or IDs:
{"username": "jennykim", "impersonator": "hue", "eventTime": 1444243437834, "operationText": "", "service": "accounts", "url": "/accounts/login/", "allowed": true, "operation": "USER_LOGIN", "ipAddress": "127.0.0.1"}
{"username": "jennykim", "impersonator": "hue", "eventTime": 1444243464043, "operationText": "Created User with username: yoshi", "service": "useradmin", "url": "/useradmin/users/new", "allowed": true, "operation": "CREATE_USER", "ipAddress": "127.0.0.1"}
{"username": "jennykim", "impersonator": "hue", "eventTime": 1444243475043, "operationText": "Edited User with username: yoshi", "service": "useradmin", "url": "/useradmin/users/edit/yoshi", "allowed": true, "operation": "EDIT_USER", "ipAddress": "127.0.0.1"}
{"username": "jennykim", "impersonator": "hue", "eventTime": 1444243489821, "operationText": "Created Group: hue, with member(s): hue, jennykim", "service": "useradmin", "url": "/useradmin/groups/new", "allowed": true, "operation": "CREATE_GROUP", "ipAddress": "127.0.0.1"}
{"username": "jennykim", "impersonator": "hue", "eventTime": 1444243501681, "operationText": "Edited Group: hue, with member(s): hue, jennykim", "service": "useradmin", "url": "/useradmin/groups/edit/hue", "allowed": true, "operation": "EDIT_GROUP", "ipAddress": "127.0.0.1"}
{"username": "jennykim", "impersonator": "hue", "eventTime": 1444243507026, "operationText": "Deleted Group(s): hue", "service": "useradmin", "url": "/useradmin/groups/delete", "allowed": true, "operation": "DELETE_GROUP", "ipAddress": "127.0.0.1"}
{"username": "jennykim", "impersonator": "hue", "eventTime": 1444243531166, "operationText": "", "service": "accounts", "url": "/accounts/login/", "allowed": true, "operation": "USER_LOGIN", "ipAddress": "127.0.0.1"}
{"username": "jennykim", "impersonator": "hue", "eventTime": 1444243539505, "operationText": "Added/Synced LDAP username(s): cconner", "service": "useradmin", "url": "/useradmin/users/add_ldap_users", "allowed": true, "operation": "ADD_LDAP_USERS", "ipAddress": "127.0.0.1"}
{"username": "jennykim", "impersonator": "hue", "eventTime": 1444243550296, "operationText": "Added LDAP Group(s): admins", "service": "useradmin", "url": "/useradmin/users/add_ldap_groups", "allowed": true, "operation": "ADD_LDAP_GROUPS", "ipAddress": "127.0.0.1"}
{"username": "jennykim", "impersonator": "hue", "eventTime": 1444243561598, "operationText": "", "service": "useradmin", "url": "/useradmin/users/sync_ldap_users_groups", "allowed": true, "operation": "SYNC_LDAP_USERS_GROUPS", "ipAddress": "127.0.0.1"}