LPS-41340 please read comments - new staged model data handlers for asset category and vocabulary

Hey Brian,

I've started a more major refactoring and cleanup for the AssetCategory and AssetVocabulary export/import. The change is too be to send it in only one chunk, so I'm splitting it up, I think this is more easy to review. I'll send the change gradually to you once the preivious goes in if that is ok.

Thanks,

Máté

reviewed by @KocsisDaniel