Add ETag to Task upon success

On top of this change, certain method names were renamed.
StorageHandler.updateGoogleId has been renamed to
StorageHandler.updateStorages

GoogleStorage.addGoogleIdToStorage has been renamed to
GoogleStorage.updateStorages

Changes to ConcurrentDelete: It now resets the isDeleted flag to false
after a successful delete on Google’s services.

Changes to Logic: Set isModified flag as true during processEdit; Set
isDeleted flag as true during processDelete.