Allow download tracking for anonymous users

[Archinowsk]

Could it be possible to add a setting to enable download tracking for anonymous users?

Currently download tracking is only enabled for registered users:

calibre-web/cps/helper.py

Lines 1101 to 1103 in e603184

	# collect downloaded books only for registered user and not for anonymous user
	if current_user.is_authenticated:
	ub.update_download(book_id, int(current_user.id))

My use case is running a public library-kind page (https://roolipelikirjasto.fi) with only anonymous users and I would like to use the Hot Books (Most Downloaded) category and overall see download statistics.