Add tests
Remove the favorites pseudo namespace if there are no lists or tasks favorited
Regenerate swagger docs
Fix favorite lists not being updated because of nonexisting users (the favorite list does not have one)
Make the pseudo favorites list always favorited
Add favorited lists to the favorites pseudo namespace
Add favorite field to list
Co-authored-by: kolaente <k@knt.li>
Reviewed-on: vikunja/api#654
