Folders

This PR brings in further integration for OAE in the following aspects:
 - Activities
 - Search
 - Previews
 - REST Docs
 - Extra functionality such as updating, deleting, ..
`oae-library/lib/api.search#registerLibrarySearch` used to check that the libraryOwnerId was a user or principal. If it wasn't it returned a 400. Because folders (and possible other libraries) need to be accommodated, that check has been removed. We could add an extra validate option or implement a `getLibraryOwner` for `content-library` searches that does some extra validation on the `libraryOwnerId`, but I didn't think it was worth the effort...