[#653] Support for RAW DATA export/import on non-monitoring groups

* When building the RAW DATA report, we need to query the Survey Group
  to know if is a _Monitoring_ group
* If is a monitoring group, we need to export 2 columns, `Identifier`
  and `Display Name`, otherwise we just keep with the old process
* When importing a RAW DATA report, we need to check if the spreadsheet
  contains the 2 extra columns
* We know the fragility of business logic based on indices, instead of
  the actual content of the column, but we're not adding more
  fragility to this process, it's fragile already ;)
[#653] Code improvement

* Based on code review from @muloem
[#653] Code cleanup based on code review

* The JSON.isNull() also checks the non-existence of a key
Merge pull request #654 from akvo/issue/653

[#653] Support for RAW DATA export/import on non-monitoring groups