add serialisation for new QGLikelihoodObject

Update for BOOSTIO branch - please merge soon.
- add serialisation for new QGLikelihoodObject in JetMetObjects
- replace dash with empty string in label name before returning to the user
  Oracle interprets empty string as NULL so this can't be used as labelName
  in the DB, so internally we use a '-'. This commit makes sure that the user 
  still sees an emtpy string.