added APIs related to group&invite on OCAccountManager

added APIs related to group&invite on OCAccountManager

According to the OCF cloud specification, I implemented new 15 APIs
related to group and invite.
: createGroup, getGroupList, deleteGroup, joinGroup, addDeviceToGroup,
  getGroupInfo, leaveGroup, deleteDeviceFromGroup, observeGroup,
  cancelObserveGroup, observeInvitation, cancelObserveInvitation,
  sendInvitation, cancelInvitation, deleteInvitation

Change-Id: I29e4cb8839d254a58be48b04d0fef35e6fbb2867
Signed-off-by: Jaewook Jung <jw0213.jung@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/10149
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jaehong Jo <jaehong.jo@samsung.com>
Reviewed-by: jihwan seo <jihwan.seo@samsung.com>
Reviewed-by: Ashok Babu Channa <ashok.channa@samsung.com>