Appends failonerror = false

* When copying the configuration files, set `failonerror` to false,
  to continue with the rest of files
Fixes Issue #116 - Changes the way of handling existing SurveyInstance

* If a `SurveyInstance` is preset, we check for a `QuestionAnswerStore`, if
  there is an entry for combination `SurveyInstance, Survey, Question` we skip
  processing that line, otherwise we store it.
Issue #116 - Fixes NPE when dealing with a previous SurveyInstance
Merge branch 'master' of https://github.com/akvo/akvo-flow into develop