[455] Add extra properties to translation kind

* Adds surveyId and questionGroupId to the Translation
kind, so we can retrieve translations faster. 

* Includes a method for retroactively populating these fields
for old translations.
[#455] Simplify populate new fields in Translation kind

* Using the ENUM in the switch statements directly

* Using a cursor to retrieve the translations, which is more
efficient than using offset

* Don't use backend for processing the tasks.
Merge branch 'develop' into feature/455
[#455] translation rest service to use question group id for retrieval
[#455] save questionGroupId and surveyId when new translations are made
Merge branch 'develop' into feature/455
Merge pull request #467 from akvo/feature/455

Feature/455