Merge pull request #29 from sebn/plain-app-functions

Replace app methods with plain functions
Working import/export (to be refactored)
Extract ExportController from ApplicationController
Extract loadStringFromFile() from ImportController
Extract saveStringToFile() from ExportController
Extract app.importAllFromJSON() & .exportAllToJSON() from ui
Move some core modules to core/storage submodule
Move import/export logic to stores