[Cleanup] Remove unused import
Issue #275 - Add apiKey as parameter

* The import process makes API calls to the source instance. This
  requests requires to be authenticated
* We have enabled REST security on _classic_ api
* The process doesn't have a way to know the API key of the source (it
  could be any other instance)
* The user is required to pass the apiKey as GET parameter
Issue #275 - Append apiKey param to the Task builder
Issue #265 - Call invalidate report when deleting a SurveyInstance

* The DELETE method now triggers a `invalidate` message when the user
  deletes a survey instance from the UI
Issue #225 - use Ember.none instead of compare to null
Merge branch 'develop' of https://github.com/akvo/akvo-flow into develop
Merge branch 'master' into develop
Merge after survey_report update.