LPS-32783 DL refactoring for new staging

Hey Julio,

This is the change set for the DL portlet refactoring to the new staging environment.

It follows the pattern what we have had previously as well, there are some minor tuning in the system.

One is that now we have the possibility to override a class' default StagedModelDataHandler. This is needed because the system be default is designed to get a model's modelClassName and then find the SMDH based on that, but for the LiferayFileEntry it's returning the DLFileEntry as a model class name which is not true, and we need that to channel through the FileEntryStagedModelDataHandler instead.

The other are quite straightforward I think, but if you have any questions of course just let me know.

Thanks,

Máté