added APIs related to account in OCAccountManager

added APIs related to account in OCAccountManager

added 2 APIs related to account
: searchUser, deleteDevice

and modified signOut API due to the change of the specification
that signOut message has no more any payload but only login property.

Change-Id: Ida9abb953d1bed0dae0fb4f0cb2bed522bc8a3dd
Signed-off-by: Jaewook Jung <jw0213.jung@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/10171
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jee Hyeok Kim <jihyeok13.kim@samsung.com>