LPS-27530 BookmarksFolder changes for new staging

Hey Julio,

This is a next step in pushing in the bookmarks changes to trunk. In this PR you will find the same pattern we followed for the BookmarksEntry: copying the logic over, applying the new logic, leaving the portlet data handler untouched for now.

Please note that this PR is independent from the BookmarksEntry changes, meaning that the portal will compile and work properly on either set of changes. So these two can be merged separately as well, they does not affect the same set of code now.

The bookmarks portlet data handler changes will follow as soon as the staged model data handlers are in. And the test as well.

Cheers,

Máté