* Implemented deferred (late) producer registration.
* Consolidated write(OFMessage, FloodlightContext) and
  write(List<OFMessage>, FloodlightContext); the latter now invokes
  the former.
* Removed (currently) unused interface.
* Added flush () to write (List<OFMessage>, FloodlightContext).
Merge pull request #365 from mwfong/producerconsumer

OFSwitchBase write() Consolidation