ME:DW Added a better way to get the choices
ME|DW: refactored the retrieval of choices field
DW:ME Code refactor
ME:JZ:DW Tested with mali dataset
DW: returns a the field name if no labes are found
DW: removed label for key
DW: Check for choices in survey object
DW: Corrected the failing tests
DW: Removed case insensitive check
PLD: get returns None as default
Merge pull request #749 from onaio/722_charts_api_blank_fields

722 charts api blank fields