'Extension' package content to be refined

[sgrellet]

Currently it’s almost raw EPOS conceptual model but most of the IE discussion is about 'core'. + also not being intrusive into pre-existing communities standards.
There may be a need to keep some classes from EPOS conceptual model where no community standard exist (at least just some classes as placeholders and not too much attributes detailing them).
Anyhow all this would ultimately be taken on board a SWG down the road for finalisation