Render report form without an empty navbar

It just restricted the width of the table, without putting any
actual context info there, so it was pointless...
Make conference reports more filterable

For all fields where we could previously just filter on "must exist",
we'll now dynamically show a textbox that lets you filter (using a
cast insensitive contains operation) on the contents in it. Keep the
checkbox checked and leave the textbox empty for the old behaviour of
just checking if a field is defined.