LPS-33228 Making RepositoryModel a StagedGroupedModel

Hey Julio,

I've sent you this set of changes a while ago, and we have agreed that I'm going to re-send this to you with splitting the commits - returning null in the CMIS related clone methods, then in a separate commit I'm adding a comment and the code, why I think it's good to have the code there instead of returning just a null.

The original debate was to return null or not in the CMIS* clone methods because they never supposed to be called.

The reason I haven't sent this to you earlier is because we thought we won't need this, but later on we discovered that we will.

So here it goes :)

Thanks,

Máté

cc: @KocsisDaniel