This differential modifies TemporaryMesssageStorage API. Changes are:
1. Public API does not allow to create TemporaryMessageStorage at an arbitrary disk location. There are just two locations: one for messages with messageInfos and the other for rescinds.
2. Location for rescinds will use different directory and will prefix semaphores with differenti strings.
REMINDER: On iOS we can't store messages in SQLite directly from Notification Service. We agreed on workaround where NotificationService stores messages in a temporary flat file. AppDelegate reads and then removes (clears) content of this file when app is launched and transfers messages to the database. The class being subject of this differential provides an API to do that. Initially it was used exclusively for visible notifications since rescinds were handled by AppDelegate, Now that rescinds are handled by NSE we have to store them in a flat file as well so that AppDelegate can read them and update `unread` statuses of relevant threads on App start.