Tentative fix for  multiple launches of sync, linked to issue #26, and
tentative fix for issue #25 (the next QuestionActivity started and
touched its question before the previous had saved, making the previous
clear questionLocationCallback after the next had started)
Fix caught back button press
Fix threadsafe issues with models, storage, LocationService, and
StatusManager, all related to issue #25. Add caching capability to
storage, for performance.
Merge pull request #48 from wehlutyk/feature/background-bugs

Feature/background bugs
Merge branch 'develop' into feature/documentation