UK: add get_survey_element and get_choice_label to data dictionary
UK: set label for select one fields in /stats/submissions endpoint, closes 361
PLD: pull tutorial from ona
PLD: use get default arg
PLD: it makes 4 submissions and groups by a constant field, so we expect count 4
Merge pull request #362 from onaio/361-choice-label-stats-endpoint

set label for select one fields for /stats/submissions endpoint