LPS-51795 Basic stuff for lifecycle handling during export/import

Hey Brian,

This is the first batch of a series of changes. We have been planning a sort of lifecycle event handling for export and import - we have had earlier some code pieces serving this, but we wanted a more sophisticated solution developers can use to react on certain events during a publication or an export import.

These changes provide the base for it. More to follow.

Thanks,

Máté