Annotation search: fix bug preventing more than one "include sub-annotation"

Even though additional annotation filters could be added, checking "Include
sub-annotations" did not have any effect for the new filters. This commit fixes
this problem by giving a new sub-annotation control a proper name and by making
the query generation aware of the fact that there can be more than one of these
fields.

Thanks to Casey Schneider-Mizell for reporting this bug. This commit fixes #655.