Add new resource property 'EXPLICIT_DISCOVERABLE'

Add new resource property 'EXPLICIT_DISCOVERABLE'

Some resources (such as, SVR's) needs to be discovered only when
explicitly requested. This property allows the resource to be included
in discovery response only when explicitly requested via query filters.

Change-Id: I1adeffa0996ecf36ffdd9ebd3dbf9c32d9f3cc0d
Signed-off-by: Sachin Agrawal <sachin.agrawal@intel.com>
Signed-off-by: Sakthivel Samidurai <sakthivel.samidurai@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1680
Reviewed-by: Joseph Morrow <joseph.l.morrow@intel.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Randeep Singh <randeep.s@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1952