[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
[#449] Adds missing translation key

* `ant translate` also removes unused keys
Merge branch 'develop' into feature/455
[#464] Exclude __MACOSX when processing folders duing bulk upload

* More info on __MACOSX
  http://old.floatingsun.net/2007/02/07/whats-with-__macosx-in-zip-files/
[#465] Change settings for uploading chunks

* Set Resumable.js `simultaneousUploads` to 1
* Define a timeout of 500ms before sending the notification
Merge pull request #467 from akvo/feature/455

Feature/455
Release notes v1.6.11
[#455] Populate surveyId and questionGroupId when copying surveys
[#471] Adds Known issues section
Merge branch 'develop'