Move worker code to package and add README

indexedDb/channels/handlers.go

indexedDb/channels/main.go

indexedDb/dm/handlers.go

indexedDb/dm/main.go

indexedDbWorker/channels/implementation.go

indexedDbWorker/channels/init.go

indexedDbWorker/dm/implementation.go

indexedDbWorker/dm/init.go

worker/README.md

worker/manager.go

worker/manager_test.go

worker/tag.go

worker/thread.go