implement empty_data_fields_hidden flag in the query

The result of the query is still a mixed list of questions and
answers, but it excludes questions which are unanswered.
commas, because syntax
fix a few things
tweak the query when edfh=1
Merge branch 'ahj-view-empty-questions-filtered-in-query' into devel

Conflicts:
	website/views/AHJ.py

Fixes #36