UK: delete temp file after export
UK: remove attachment.full_filepath, prevent creation of unnecessary temp files
UK: pep8
UK: compare sorted values
UK: use try .. finally to close temp_file
UK: code refactor: ensure file is closed properly
PLD: remove unused streaminghttpresponse
PLD: use helper to build HttpResponse
PLD: close zips if finally if not none
Merge pull request #387 from onaio/fix-memory-issues

delete tmp files after use for attachment export