Add EntityHandler callback parameter to C SDK.

Add EntityHandler callback parameter to C SDK.

Allows C api users to have a context callback parameter
with the use of EntityHandler callbacks for OCCreateResource.

Change-Id: I1358b6dbd5c2a9a1940f6146a87aacf84c16bb3c
Signed-off-by: Charlie Lenahan <charlie.lenahan@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1042
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Gabriel Schulhof <gabriel.schulhof@intel.com>
Reviewed-by: Patrick Lankswert <patrick.lankswert@intel.com>