add more explicit err msg to stacktrace when MediaManagerApiCore throws config error
add test/config.js to simplify config of MediaManagerCoreApi in tests
Added initial impl of ImportersImages_transform_test.js
refine ImportersImages_transform_test.js
rename ImportBatch.ended_at|get/setEndedAt() to ImportBatch.completed_at|get/setCompletedAt()
rename ImageService.batchImportFs to ImageService.importBatchFs