Added missing thing type package (#370)

Author: tomhoefer

org.openhab.binding.zigbee/META-INF/MANIFEST.MF

@@ -55,6 +55,7 @@ Service-Component: OSGI-INF/*.xml
 Export-Package: org.openhab.binding.zigbee,
  org.openhab.binding.zigbee.converter,
  org.openhab.binding.zigbee.discovery,
- org.openhab.binding.zigbee.handler
+ org.openhab.binding.zigbee.handler,
+ org.openhab.binding.zigbee.thingtype
 Bundle-ClassPath: .
 Bundle-ActivationPolicy: lazy