Description of problem:
[DEV] only!
At the moment for each user in same workspace, we publish user's selected translation unit and broadcast the event to the whole workspace domain. This is to be able to detect concurrent editing of same translation by multiple users. However what we really need to broadcast is just the translation unit's id not the whole object. 

Version-Release number of selected component (if applicable):
2.0 and below

How reproducible:
n/a

Steps to Reproduce:
n/a
  
Actual results:
entire translation unit is broadcasted and wasted bandwidth and memory. 

Expected results:
only broadcast translation unit id.

Additional info:
@see org.zanata.webtrans.server.TranslationWorkspace
@see org.zanata.webtrans.shared.rpc.TransUnitEdit
@see org.zanata.webtrans.server.TranslationWorkspaceImpl
@see org.zanata.webtrans.shared.model.PersonSessionDetails