Quite easy, just need to list the field. Turns out the fields argument
isn't needed for custom filters. Removed updated_since and
submitted_since from the fields array then.

Well, on second thoughts, I need to have special "self" value that
matches all people linked to the current user (there can be many).

For that to work, I also need a specialization of the
DjangoFilterBackend that passes the request along.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>