Only mark entries as read when scrolling down
Calculate number of unread articles

Right now it does not get updated, but that is ok for now
Split function into distinct submethods

Found missing return 404s by doing so
Only render the count to the active category
Change the amount of unread entries in a category
Flush the entitymanager when updating an entry

Maybe this solves the off-by-one problem when returning the amount unread entries after
marking one as read
Add model classes to persistence.xml and exclude everything else

I'm sure I did this already, but the lines were missing